Electric machine with multi-part trapezoidal teeth

ABSTRACT

An electric machine may include an stator and a rotatable rotor. At least one of the stator or the rotor may include a plurality of multi-part trapezoidal teeth with an electromagnetic coil disposed around each tooth.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 18/104,426, filed Feb. 1, 2023, which is acontinuation application of U.S. patent application Ser. No. 17/882,947,filed Aug. 8, 2022 (now U.S. Pat. No. 11,594,920), which is acontinuation application of U.S. patent application Ser. No. 17/493,089,filed Oct. 4, 2021 (now U.S. Pat. No. 11,451,099), which claims priorityto International Application No. PCT/IB2021/058475, filed Sep. 17, 2021,which claims priority to U.S. Provisional Patent Application No.63/081,043, filed Sep. 21, 2020, each of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a radial flux electric machine.

BACKGROUND

The current disclosure relates to electrical machines, and in particularto radial flux electrical machines. Electric machine (or electricalmachine) is a general term for machines that rely on electromagneticforces for its operation. The two main parts of an electric machine canbe described in mechanical or electrical terms. In mechanical terms, therotor is the rotating part, and the stator is the stationary part of anelectrical machine. In electrical terms, the armature is thepower-producing component and the field is the magnetic field producingcomponent of an electrical machine. The armature can be on the rotor orthe stator, and the magnetic field can be provided by eitherelectromagnets or permanent magnets mounted on either the rotor or thestator. Electric machines are electromechanical energy converters andinclude, among others, electric motors, and electric generators. Anelectric motor converts electricity to mechanical power while anelectric generator converts mechanical power to electricity. The movingpart of the electric machine can be rotating (rotating electricmachines) or linear (linear electric machines). Electric machinesoperate on the principle that electrical current generateselectromagnetic flux and vice versa. In some electric machine, a rotorcomprising permanent magnets is configured for rotating in anelectromagnetic field generated by a plurality of electromagnets throughwhich electricity is passed.

Electrical machines can be categorized as axial flux electric machinesand radial flux electric machines. The fundamental difference betweenthese types of machines lie in the orientation of the magnetic field inthese machines. In radial flux electric machines, the working magneticflux crosses the air gap between the stator and the rotor in the radialplane, while in axial flux electric machines, the magnetic flux crossesthe air gap parallel to the axis of rotation. A large number ofsolutions are known aimed at reducing the stray fields of permanentmagnets and windings of an electric machine, as well as increasing theconcentration of the magnetic flux density in the stator and rotorcores, and strive to ensure the same values of the magnetic flux densityin all parts of the core. There are also a large number of solutionsaimed at providing a high fill factor for permanent magnet electricmachines. Some of these solutions use complex tooth shapes to improveelectric machine performance. While some of these solutions effectivelyuses the volume of the tooth, they do not sufficiently reduce theleakage fluxes of the electric machine. In addition, in some cases, thecomplex tooth shapes makes it difficult to provide a high winding fillfactor for electric machines. The radial flux electric machines of thecurrent disclosure alleviates some or all of the above-mentioned issues.A decrease in leakage fluxes and an increase in the fill factor inembodiments of electric machines of the current disclosure may allow forincreased power and efficiency of electrical machines. However, thescope of the current disclosure is defined by the claims and not by theability to solve any problem.

SUMMARY

Several embodiments of an electric machine and methods of fabricatingand using an electric machine are disclosed. It is to be understood thatboth the foregoing general description and the following detaileddescription are exemplary and explanatory only. As such, the scope ofthe disclosure is not limited solely to the disclosed embodiments.Instead, it is intended to cover such alternatives, modifications andequivalents within the spirit and scope of the disclosed embodiments.Persons skilled in the art would understand how various changes,substitutions and alterations can be made to the disclosed embodimentswithout departing from the spirit and scope of the disclosure.

In one embodiment, an electric machine having a plurality of trapezoidalteeth is disclosed. The electric machine may include a plurality ofelectromagnetic coils. Each coil may include a non-uniform trapezoidalcavity therethrough and may be configured to contain therein one toothof the plurality of teeth. Each tooth may be formed of multiple piecesthat, when assembled together form a trapezoidal tooth.

In some embodiments, the trapezoidal shape of the multipiece tooth, inwhich the cross-sectional area increases in the radial direction towardsthe rotor, and the winding coils are shifted as close as possible to theair gap, may significantly reduce the leakage fields of the electricmachine. Pre-forming a tooth with a constant cross-sectional perimeterin the radial direction leads to an increase in the fill factor of theelectric machine and improves the performance, efficiency torque andpower of the electric machine.

In one embodiment, a radial flux electric machine is disclosed. Theelectric machine may include a rotor configured to rotate about an axisof rotation and a stator. At least one of the rotor or the stator mayinclude a plurality of teeth annularly arranged about the axis ofrotation. The electric machine may also include a plurality ofelectromagnetic coils. Each coil of the plurality of electromagneticcoils may have a non-uniform trapezoidal cavity therethrough. Eachcavity may be configured to contain therein one tooth of the pluralityof teeth. Each tooth of the plurality of teeth may be formed of multiplepieces that, when assembled together correspond to a shape of thenon-uniform trapezoidal cavity.

Various embodiments of the electric machine may alternatively oradditionally include one or more of the following aspects: when themultiple pieces of each tooth are assembled together, an externalperimeter of each tooth corresponds to an internal perimeter of thecavity of a corresponding coil; each tooth includes a core tooth-portionand at least one wedge-shaped portion; each tooth includes a coretooth-portion and at least two wedge-shaped portions disposed onopposite sides of the core portion; in a plane perpendicular to the axisof rotation, the core tooth-portion has a substantially rectangularcross-sectional shape and the at least one wedge-shaped portion has asubstantially triangular cross-sectional shape; in a plane perpendicularto a radial direction, the core tooth-portion and the at least onewedge-shaped portion has a substantially rectangular cross-sectionalshape; the core tooth-portion and the at least one wedge-shaped portionof each tooth are coupled together using an adhesive material; the coretooth-portion of each tooth is integrally formed with an annular ringthat extends around the axis of rotation; when the multiple pieces ofeach tooth are assembled together, each tooth defines external surfaceshaving two sets of opposing faces, the opposing faces of each set of thetwo sets being non-parallel to each other; the opposing faces ofadjacent teeth are parallel to each other; each face of the two sets ofopposing faces is inclined in a radial direction; the opposing faces ofone set of opposing faces converge towards each other in a radiallyoutward direction and the opposing faces of the other set of opposingfaces diverge from each other in the radially outward direction; across-section of each tooth in a plane perpendicular to the axis ofrotation has a trapezoidal shape, and a cross-section of each tooth in aplane perpendicular to a radial direction has a rectangular shape; aperimeter of the cross-sections perpendicular to a radial direction issubstantially a constant in the radial direction; an area of thecross-sections perpendicular to the radial direction varies in theradial direction; the stator includes the plurality of teeth, and thearea of the cross-section perpendicular to the radial directionincreases in the radial direction towards the rotor; a cross-section ofeach tooth in an axial plane has an isosceles trapezoidal shape; atleast one piece of the multiple pieces of each tooth is formed of a softmagnetic composite (SMC); the stator includes the plurality of teeth,and wherein a first piece of the multiple pieces of each tooth isintegral with and extends radially from an annular stator ring thatextends around the axis of rotation, and a second piece of the multiplepieces of each tooth is non-integrally formed with the first piece; theelectric machine is one of an electric motor or an electric generator.

In another embodiment, a radial flux electric machine is disclosed. Theelectric machine may include a rotor configured to rotate about an axisof rotation and a stator fixedly positioned proximate the rotor. Atleast one of the rotor or the stator may include a plurality of teethannularly arranged about the axis of rotation. Each tooth of theplurality of teeth may extend in a radial direction such that aplurality of cross-sectional areas of each tooth in a plurality ofplanes perpendicular to the radial direction may vary. And perimeters ofthe plurality of cross-sections may be substantially the same across theplurality of perpendicular planes.

Various embodiments of the electric machine may alternatively oradditionally include one or more of the following aspects: a shape ofeach tooth in at least one of an axial plane or a radial plane of theelectric machine is a trapezoid; the shape of each tooth in at least oneof an axial plane or a radial plane of the electric machine is anisosceles trapezoid; the plurality of teeth are annularly arranged onthe stator; the rotor is disposed radially outwards of the stator, awidth of each tooth in a radial plane increases in the radial directiontowards the rotor, and a length of each tooth in an axial planedecreases in the radial direction towards the rotor; each tooth extendsin the radial direction such that a cross-sectional area of each toothin a plane perpendicular to the radial direction increases in the radialdirection toward the rotor; the rotor is disposed radially inwards ofthe stator, and a cross-sectional area of each tooth of the plurality ofteeth in a plane perpendicular to the radial direction increases in theradial direction toward the rotor; the plurality of teeth are annularlyarranged on the rotor; the electric machine further includes a pluralityof electromagnetic coils, and wherein each coil of the plurality ofelectromagnetic coils extends around a separate tooth of the pluralityof teeth; each coil includes copper wire having one of a square,rectangular, or circular cross-sectional shape; the wire is multi-strandand each coil is wound in the form of a spiral in the radial directionalong a tooth; each coil includes copper foil wound around a tooth suchthat a flat side of the foil extends over an entire length of the toothin the radial direction; each coil includes a rib of copper foil woundin the form of a spiral in the radial direction along a tooth; eachtooth includes a soft magnetic composite (SMC) material; each toothincludes multiple pieces coupled together; the multiple pieces include acore portion integrally formed with an annular ring that extends aroundthe axis of rotation and one or more wedge portions coupled to the coreportion; the one or more wedge portions include at least two wedgeportions disposed on opposite sides of the core portion; the electricmachine is an electric motor or an electric generator; one of the statoror the rotor includes an outer part and an inner part and wherein thestator and rotor are separated by a double air gap; the outer part andthe inner part connected together by a connecting portion made of amagnetically conductive material.

In another embodiment, a radial flux electric machine is disclosed. Theelectric machine may include a rotor configured to rotate about an axisof rotation, a plurality of electromagnetic coils, and a stator. Thestator may include an annular stator ring extending about the axis ofrotation and a plurality of multi-part teeth circumferentially arrangedon the stator ring. Each multi-part tooth of the plurality of multi-partteeth may include a core tooth-portion integrally formed with the statorring and at least one additional tooth-portion separate from the statorring. Each coil of the plurality of electromagnetic coils may be mountedon a different multi-part tooth of the plurality of multi-part teethsuch that each coil surrounds a corresponding core tooth-portion of themulti-part tooth with a gap between the coil and the core tooth-portion.The at least one additional tooth-portion may be disposed in the gap.

Various embodiments of the electric machine may alternatively oradditionally include one or more of the following aspects: the coretooth-portion each multi-part teeth is formed of a soft magneticcomposite (SMC); the annular stator ring is formed of a soft magneticcomposite (SMC); the annular stator ring includes two mirror-symmetrichalves coupled together along a plane of symmetry perpendicular to theaxis of rotation; the two mirror-symmetric halves are attached togetheralong the plane of symmetry using an adhesive material; the annularstator ring includes multiple axially stacked annular rings, at whereinat least two of the stacked annular rings are made of a soft magneticcomposite (SMC); the core tooth-portion of each multi-part tooth extendsoutward in a radial direction from the annular stator ring; across-sectional of each of the core tooth-portion and the at least oneadditional tooth-portion along a plane perpendicular to the radialdirection has a substantially rectangular shape; a cross-section of thecore tooth-portion along a plane perpendicular to the axis of rotationhas a substantially rectangular shape; a cross-section of the at leastone additional tooth-portion along the plane perpendicular to the axisof rotation has a substantially triangular shape; a cross-sectional ofeach tooth of the plurality of multi-part teeth along the planeperpendicular to the axis of rotation has a substantially trapezoidalshape; the at least one additional tooth-portion includes a pair ofadditional tooth-portions arranged symmetrically on opposite sides ofthe core tooth-portion; the core tooth-portion and the at least oneadditional tooth-portion of each tooth of the plurality of multi-partteeth are coupled together using an adhesive material; a differencebetween coefficients of thermal expansion of materials of the coretooth-portion, the at least one additional tooth-portion, and theadhesive material is less than about 20%; the at least one additionaltooth-portion of each multi-part tooth is wedged between an internalsurface of a coil of the plurality of electromagnetic coils and anexternal surface of the core tooth-portion; a coil of the plurality ofelectromagnetic coils surrounds the core tooth-portion of each toothsuch that at least two gaps are formed between an inner surface of thecoil and opposite sides of the core tooth-portion, and wherein the atleast one additional tooth-portion includes at least two additionaltooth-portions disposed in a different gap of the at least two gaps; across-section of each multi-part tooth of the plurality of multi-partteeth in a plane perpendicular to a radial direction has a rectangularshape; a perimeter of the cross-section is substantially a constant inthe radial direction; an area of the cross-section varies in the radialdirection; the electric machine is an electric motor or an electricgenerator.

In another embodiment, a radial flux electric machine is disclosed. Theelectric machine may include a rotor configured to rotate about an axisof rotation, a plurality of electromagnetic coils, and a stator. Thestator may have an annular stator ring and a plurality of coretooth-portions extending in a radial direction. The annular stator ringand the plurality of core tooth-portions may be integrally formed of aSoft Magnetic Composite (SMC). The SMC may include one or more isotropicferromagnetic materials, a magnetic saturation induction of greater thanor equal to about 1.6 Tesla, and an electrical resistivity greater than10 micro-ohm/m.

Various embodiments of the electric machine may alternatively oradditionally include one or more of the following aspects: the statorincludes a plurality of multi-part teeth symmetrically arranged on theannular stator ring, wherein each tooth of the plurality of multi-partteeth includes one of the plurality of core tooth-portions and at leastone additional tooth-portion non-integrally formed with the one of theplurality of core tooth portions; a pair of additional tooth-portionsare arranged on opposite sides of an associated core tooth-portion; across-section of the core tooth-portion of each tooth along a planeperpendicular to the axis of rotation has a substantially rectangularshape, and a cross-section of each additional tooth portion of the atleast one additional tooth-portions along the plane perpendicular to theaxis of rotation has a substantially triangular shape; a cross-sectionof each of the core tooth-portions and the at least one additionaltooth-portions along a plane perpendicular to the radial direction has asubstantially rectangular shape; a cross-section of each tooth of theplurality of multi-part teeth in a plane perpendicular to the axis ofrotation has a trapezoidal shape; a cross-section of each tooth of theplurality of multi-part teeth in a plane perpendicular to the radialdirection has a substantially rectangular shape, and a perimeter of thecross-section is substantially a constant in the radial direction, andan area of the cross-section varies in the radial direction; the rotoris disposed radially outwards of the stator to form an air gap betweenthe rotor and the stator, and the area of the cross-section increases inthe radial direction toward the air gap; each tooth of the plurality ofmulti-part teeth defines external surfaces having two sets of opposingfaces, the opposing faces of each set of the two sets being non-parallelto each other, and adjacent side faces of adjacent teeth being parallelto each other; each face of the two sets of opposing faces is inclinedin a radial direction; the opposing faces of one set of opposing facesconverge towards each other in a radially outward direction and theopposing faces of the other set of opposing faces diverge from eachother in the radially outward direction; the at least one additionaltooth-portions is formed of the SMC; at least one additionaltooth-portion is formed of an isotropic material other than SMC; theannular stator ring includes two mirror-symmetric bodies coupledtogether along a plane of symmetry perpendicular to the axis ofrotation; the two mirror-symmetric bodies are attached together alongthe plane of symmetry using an adhesive material, wherein a differencebetween coefficients of thermal expansion of the SMC and the adhesivematerial is less than about 20%; the magnetic saturation induction ofthe SMC is greater than or equal to about 2.4 Tesla; the magneticsaturation induction of the SMC is greater than or equal to about 2.5Tesla; the resistivity of the SMC is greater than about 100 micro-ohm/m;the electric machine is an electric motor; the electric machine is anelectric generator.

In another embodiment, a radial flux electric machine is disclosed. Theelectric machine may include an inner stator and an outer rotorconfigured to rotate about the stator. The outer rotor may include arotor base and a plurality of annularly arranged permanent magnetsaxially extending from the rotor base parallel to an axis of rotation ofthe rotor. A cylindrical core may extend from the rotor base encirclingthe plurality of permanent magnets. The core may be formed of a SoftMagnetic Composite (SMC). A sleeve may encircle the rotor. The sleevemay support the cylindrical core and the cylindrical core may supportthe plurality of permanent magnets. The cylindrical core may bepositioned radially between the sleeve and the plurality of permanentmagnets.

Various embodiments of the electric machine may alternatively oradditionally include one or more of the following aspects: at least oneof the sleeve or the rotor base is made of non-magnetic material; thenon-magnetic material is a composite material including at least one ofcarbon fiber, glass fiber, or aramid fiber; the non-magnetic materialincludes at least one of stainless steel or aluminum; the sleeve is madeof a magnetic material; the magnetic material includes a soft magneticmaterial including laminated electrical steel sheets; the magneticmaterial is a solid body made of steel; the sleeve includes stiffeningribs disposed on recesses formed on an external surface of thecylindrical core; the cylindrical core extends from a first end coupledto the rotor base to a second end, wherein the sleeve includes abalancing ring located at the second end of the cylindrical core, andwherein the balancing ring is configured to provide dynamic balancing ofthe rotor; the sleeve extends over the balancing ring; the balancingring is formed of a non-magnetic material; the plurality of permanentmagnets are arranged on the rotor base in a substantially circularpattern around the axis of rotation; the plurality of permanent magnetsare arranged on the rotor base such that the magnetic axis of eachpermanent magnet of the plurality of permanent magnets intersect at theaxis of rotation; the rotor base is formed of aluminum or steel; therotor base includes air vents configured to direct airflow along theaxis of rotation when the rotor base rotates; the rotor base is integralwith the sleeve and the balancing ring; the plurality of permanentmagnets are attached to the cylindrical core using an adhesive, andwherein a difference between coefficients of thermal expansion ofmaterials of the plurality of permanent magnets, the cylindrical core,and the adhesive is less than about 20%; the sleeve is integral with therotor base to form a single piece; the cylindrical core and the sleeveboth have a non-uniform radial thickness about the axis of rotation, andwherein thicker regions of the sleeve are located adjacent to a centerof each permanent magnet; and the electric machine is one of electricmotor or an electric generator.

In some embodiments, a method of assembling a coil on anirregular-shaped multi-part tooth of an electric machine is disclosed.The method may include inserting at least one wedge-portion of themulti-part tooth into an opening of the coil such that a broader end ofthe at least one wedge-portion extends out of the opening in the coil.The method may also include mounting the coil with the inserted at leastone wedge-portion on a core tooth-portion of the multi-part tooth suchthat the broader end of the at least one wedge-portion remains extendedout of the opening in the coil, exerting a force on the broader end ofthe at least one wedge-portion to tighten the coil on the multi-parttooth.

Various embodiments of the disclosed method may alternatively oradditionally include one or more of the following aspects: exerting aforce on the broader end of the at least one wedge-portion includespushing the broader end of the at least one wedge-portion into theopening in the coil; the opening in the coil extends from a first end toa second end, wherein inserting the at least one wedge-portion includesinserting the at least one wedge-portion into the opening such that thebroader end extends out of the second end of the opening, and exertingthe force includes pushing the broader end towards the first end of theopening; the opening in the coil extends from a first end to a secondend, wherein a width of the opening at the first end differs from thewidth of the opening at the second end, and wherein a length of theopening at the first end differs from a height of the opening at thesecond end; a shape of the opening at the first end and the second endis rectangular; a perimeter of the opening at the first end issubstantially the same as the perimeter of the opening at the secondend; an area of the opening at the first end varies from the area of theopening at the second end; an area of the opening increases from thefirst end to the second end; inserting the at least one wedge-portioninto the opening of the coil includes inserting at least twowedge-portions into the opening; mounting the coil includes mounting thecoil on the core tooth-portion such that the core tooth-portion isdisposed between the at least two wedge-portions; using an adhesivematerial to attach the at least two wedge-portions and the coretooth-portion of the multi-part tooth together; the multi-part tooth isa part of a stator of the electric machine; the core tooth-portion ofthe multi-part tooth is one of a plurality of core tooth-portionssymmetrically arranged on an annular stator ring that extends around acentral axis, and wherein the core tooth-portion extends outward in aradial direction from the annular stator ring; the plurality of coretooth-portions are integrally formed with the annular stator ring; in aplane perpendicular to the central axis, the core tooth-portion has asubstantially rectangular cross-sectional shape and the at least onewedge-portion has a substantially triangular cross-sectional shape; in aplane perpendicular to the radial direction, the core tooth-portion andthe at least one wedge-portion have a substantially rectangularcross-sectional shape; the coil includes a winding of a copper wirearound the opening, the wire having one of a square, rectangular, orcircular cross-sectional shape; the coil includes a winding of a copperstranded wire in a spiral around the opening; the electric machine is anelectric motor; and the electric machine is an electric generator.

In some embodiments, a method of fabricating a coil for mounting on atooth of a stator or a rotor of an electric machine is disclosed. Themethod may include winding a wire about a mandrel to form a coil havinga first shape corresponding to the shape of the mandrel, removing thecoil having the first shape from the mandrel, and applying a mechanicalforce on the coil to change the shape of the coil from the first shapeto a second shape. The second shape may correspond to the shape of thetooth. The method may also include mounting the coil of the second shapeon the tooth.

Various embodiments of the disclosed method may alternatively oradditionally include one or more of the following aspects: the wire isformed of a plurality of strands of an electrical conductor; the wire isformed by twisting together an electrical conductor or made in the formof a Litz wire; the wire has a circular cross-sectional shape; the wirehas one of a square or a rectangular cross-sectional shape; the firstshape is a cylindrical shape or any shape with a substantially constantperimeter; the second shape is a trapezoidal shape; winding the wireabout the mandrel includes winding the wire about the mandrel in aspiral pattern to form coil having an internal cavity extending from afirst end to a second end; applying a mechanical force on the coilincludes selectively increasing a size of the cavity at one of the firstend or the second end; applying a mechanical force on the coil includeschanging a shape of the internal cavity; changing the shape of theinternal cavity includes changing a cross-sectional shape of theinternal cavity along a plane perpendicular to a central axis of theinternal cavity from a circular shape to a rectangular shape; a widthand a length of the rectangular shape both vary from the first end tothe second end; a perimeter of the rectangular shape is substantially aconstant from the first end to the second end and an area of therectangular shape varies from the first end to the second end; the areaof the rectangular shape increases from the first end to the second end;changing the shape of the internal cavity includes changing a3-dimensional shape of the inner cavity from a cylindrical shape to atrapezoidal shape; applying a mechanical force on the coil includesinserting a second mandrel into the internal cavity of the coil tochange a shape of the first end of the internal cavity compared to ashape of the second end of the internal cavity; applying a mechanicalforce on the coil includes applying a first mechanical force to increasea dimension of the internal cavity at one of the first end or the secondend and a second mechanical force to decrease a dimension of theinternal cavity at the other of the first end or the second end; thefirst mechanical force acts towards a central axis of the internalcavity and the second mechanical force acts away from the central axis;applying a mechanical force on the coil includes stretching the wire ofthe coil that defines at least one of the first end or the second end ofthe internal cavity; the wire is made of copper.

In one embodiment, an electric machine is disclosed. The electricmachine may include a rotor configured to rotate about an axis ofrotation, a stator having a plurality of teeth annularly arranged on astator core about the axis of rotation, a plurality of electromagneticcoils, and a base plate. Each coil of the plurality of electromagneticcoils may be mounted on a separate tooth of the plurality of teeth, andthe base plate may be located adjacent to the plurality ofelectromagnetic coils and the stator core. The base plate may be inthermal contact with the plurality of electromagnetic coils and thestator core such that as the plurality of electromagnetic coils and thestator core heat during operation, the base plate is configured to serveas a common heat sink for the plurality of electromagnetic coils and thestator core.

Various embodiments of the disclosed electric machine may alternativelyor additionally include one or more of the following aspects: each coilof the plurality of electromagnetic coils is in contact with the baseplate directly or through a thermally-conductive material disposedtherebetween; the stator core is in contact with the base plate directlyor through a thermally-conductive material disposed therebetween;further include a motor housing thermally connected to the base plate toenable heat generated by the plurality of electromagnetic coils andstator core to be dissipated through the base plate and the motorhousing; the base plate includes a first side and a second side oppositethe first side, wherein the plurality of electromagnetic coils and thestator core are in thermal contact with the first side of the base plateand the motor housing is in thermal contact with the second side of thebase plate; the second side of the base plate includes cooling fins thatextend therefrom; the cooling fins include a plurality of pins; the baseplate includes a cylindrical hub portion extending around the axis ofrotation; the stator core includes an annular stator ring that extendsaround the cylindrical hub portion of the base plate; an inner annularsurface of the annular stator ring is in contact with an outer annularsurface of the cylindrical hub portion of the base plate directly orthrough a thermally-conductive material disposed therebetween; thestator core includes an annular stator ring that extends around the axisof rotation and each tooth of the plurality of teeth includes a coretooth-portion integral with the annular stator ring; each tooth of theplurality of teeth further includes one or more additionaltooth-portions non-integrally formed with the core tooth-portion; a pairof additional tooth-portions includes tooth-portions arranged onopposite sides of the core tooth-portion; when all the tooth parts areassembled together, each tooth defines external surfaces having two setsof opposing faces, the opposing faces of each set of the two sets beingnon-parallel to each other, and wherein each face of the two sets ofopposing faces is inclined in a radial direction; opposing faces ofadjacent teeth are substantially parallel to each other; a cross-sectionof each tooth in a plane perpendicular to the radial direction has arectangular shape, and wherein a perimeter of the cross-section issubstantially a constant in the radial direction and an area of thecross-section varies in the radial direction; the base plate is formedof aluminum; the base plate includes air vents configured to direct airto the plurality of electromagnetic coils when the rotor rotates; theelectric machine is an electric motor; the electric machine is anelectric generator.

In yet another embodiment, an electric machine is disclosed. Theelectric machine may include a rotor configured to rotate about an axisof rotation, a stator having a stator core and a plurality of teethannularly arranged on the stator core about the axis of rotation, aplurality of electromagnetic coils, and a base plate. Each coil of theplurality of electromagnetic coils may be mounted on a separate tooth ofthe plurality of teeth. The base plate may be located adjacent to theplurality of electromagnetic coils and the stator core. The base platemay have a first side and an opposing second side. The first side may bein thermal contact with the plurality of electromagnetic coils and thestator core. A liquid-coolant channel may be defined on the second sideof the base plate such that as the coils and the stator core heatsduring operation, the base plate is configured to transfer the heat to aliquid coolant in the liquid-coolant channel to dissipate heat from theplurality of electromagnetic coils and the stator core.

Various embodiments of the disclosed electric machine may alternativelyor additionally include one or more of the following aspects: each coilof the plurality of electromagnetic coils is in contact with the baseplate directly or through a thermally-conductive material disposedtherebetween; the stator core is in contact with the base plate directlyor through a thermally-conductive material disposed therebetween;further include a motor housing thermally connected to the base plate toenable heat generated by the plurality of electromagnetic coils andstator core to be dissipated through the base plate and the motorhousing; the base plate includes a first side and a second side oppositethe first side, wherein the plurality of electromagnetic coils and thestator core are in thermal contact with the first side of the base plateand the motor housing is in thermal contact with the second side of thebase plate; a wall of the liquid-coolant channel is a portion of thesecond side of the base plate directly opposite a portion of the firstside of the base plate that is in thermal contact with the plurality ofelectromagnetic coils; the liquid-coolant channel extends around theaxis of rotation and an annular region on the second side of the baseplate serves as a wall of the liquid-coolant channel; the annular regionon the second side of the base plate includes a plurality of fins thatextend into the liquid-coolant channel; the plurality of fins isarranged about the axis of rotation; further include a coolant inletconfigured to direct the coolant into the liquid-coolant channel and acoolant outlet configured to direct the coolant out of theliquid-coolant channel; the base plate includes a cylindrical hubportion extending around the axis of rotation and the stator coreincludes an annular stator ring that extends around the cylindrical hubportion of the base plate, and the liquid-coolant channel passes throughthe cylindrical hub portion along the axis of rotation; an inner annularsurface of the annular stator ring is in contact with an outer annularsurface of the cylindrical hub portion of the base plate directly orthrough a thermally-conductive material disposed therebetween; eachtooth of the plurality of teeth includes a core tooth-portion integrallyformed with the annular stator ring and at least one additionaltooth-portion non-integrally formed with the core tooth-portion; theannular stator ring and the core tooth-portion are formed of a SoftMagnetic Composite (SMC); when the core tooth-portion and at least oneadditional tooth-portion are assembled together, each tooth definesexternal surfaces having two sets of opposing faces, the opposing facesof each set of the two sets being non-parallel to each other, andwherein each face of the two sets of opposing faces is inclined in aradial direction; opposing faces of adjacent teeth are parallel to eachother; a cross-section of each tooth in a plane perpendicular to theradial direction has a trapezoidal shape, and wherein a perimeter of thecross-section is substantially a constant in the radial direction and anarea of the cross-section varies in the radial direction; the base plateis formed of aluminum; the electric machine is an electric motor; theelectric machine is an electric generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this disclosure, illustrate exemplary embodiments and, togetherwith the description, are used to explain the disclosed principles. Inthese drawings, where appropriate, reference numerals illustrating likestructures, components, materials, and/or elements in different figuresare labeled similarly. It is understood that various combinations of thestructures, components, and/or elements, other than those specificallyshown, are contemplated and are within the scope of the presentdisclosure.

For simplicity and clarity of illustration, the figures depict thegeneral structure of the various described embodiments. Details ofwell-known components or features may be omitted to avoid obscuringother features, since these omitted features are well-known to those ofordinary skill in the art. Further, elements in the figures are notnecessarily drawn to scale. The dimensions of some features may beexaggerated relative to other features to improve understanding of theexemplary embodiments. One skilled in the art would appreciate that thefeatures in the figures are not necessarily drawn to scale and, unlessindicated otherwise, should not be viewed as representing proportionalrelationships between different features in a figure. Additionally, evenif it is not specifically mentioned, aspects described with reference toone embodiment or figure may also be applicable to, and may be usedwith, other embodiments or figures.

FIG. 1 illustrates a perspective view of one embodiment of an exemplaryelectric machine consistent with the current disclosure;

FIG. 2 is a cross-sectional view of the electric machine of FIG. 1 in anaxial plane;

FIG. 3 illustrates a cross-sectional view of the electric machine ofFIG. 1 in a radial plane;

FIGS. 4A-4C illustrate differing perspective views of an exemplarystator of the electric machine of FIG. 1 ;

FIG. 5 is an exemplary schematic electrical representation of the statorof the electric machine of FIG. 1 ;

FIGS. 6A-6D illustrate exemplary coils of the electric machine of FIG. 1formed of foils;

FIGS. 7A-7E illustrate exemplary coils of the electric machine of FIG. 1formed of wire;

FIGS. 8A-8E are schematic illustrations of exemplary electric machinesconsistent with the current disclosure;

FIGS. 9-10 illustrate other exemplary electric machine consistent withthe current disclosure;

FIGS. 11-22 are schematic illustrations of further exemplary electricmachines of the current disclosure;

FIGS. 23A-23N illustrate different aspects of exemplary teeth ofelectric machines consistent with the current disclosure;

FIGS. 24A-24D illustrate the assembly of an exemplary stator of anelectric machine consistent with the current disclosure;

FIGS. 25A-25B illustrate different aspects of an exemplary stator of anelectric machine consistent with the current disclosure;

FIGS. 26A-26D illustrate cross-sectional views of an exemplary tooth indifferent planes;

FIGS. 27A-27D illustrate cross-sectional views of an exemplary tooth indifferent planes;

FIGS. 28A-31B illustrate geometric features of an exemplary tooth;

FIGS. 32A-32E illustrate exemplary embodiments of a stator core of thecurrent disclosure;

FIGS. 33A-33C illustrate different portions of an exemplary stator.

FIGS. 34A-34B illustrate an exemplary outer rotor.

FIG. 35 illustrates an exemplary shaft.

FIGS. 36-37 illustrate an exemplary outer rotor.

FIGS. 38A-38D illustrate exemplary portions of an exemplary outer rotor.

FIG. 39 illustrates an exemplary outer rotor assembly.

FIG. 40 illustrates an exemplary outer rotor.

FIG. 41 illustrates portions of an exemplary outer rotor.

FIGS. 42A-42B illustrate a cross-sectional view of an exemplary outerrotor.

FIG. 43 illustrate another exemplary outer rotor.

FIG. 44 illustrates an exemplary rotor core.

FIGS. 45A-45F are schematic illustrations of an exemplary method ofinstalling a coil on a multi-part tooth in an electric machine of thecurrent disclosure;

FIGS. 46A-46C are simplified schematic illustrations of an exemplarymethod of installing a coil on a multi-part tooth in an electric machineof the current disclosure;

FIG. 47 is a flow chart of an exemplary method of installing a coil on amulti-part tooth in an electric machine of the current disclosure.

FIGS. 48A-48D are schematic illustrations of an exemplary method offorming a coil of an electric machine of the current disclosure;

FIGS. 49A-49D are simplified schematic illustrations of an exemplarymethod of forming a coil of an electric machine of the currentdisclosure;

FIGS. 50A-50D are simplified schematic illustrations of an exemplarymethod of forming a coil of an electric machine of the currentdisclosure;

FIGS. 51A-51B are simplified schematic illustrations of an exemplarymethod of forming a coil of an electric machine of the currentdisclosure;

FIG. 52 is a flow chart of an exemplary method of forming a coil of anelectric machine of the current disclosure.

FIG. 53 illustrates a cross-sectional view of an electric machine in anaxial plane, consistent with disclosed embodiments.

FIG. 54 illustrates a perspective view of a stator of the electricmachine of FIG. 53 , consistent with disclosed embodiments.

FIG. 55 illustrates a cross-sectional view of a stator of the electricmachine of FIG. 53 in an axial plane, consistent with disclosedembodiments.

FIG. 56 illustrates a perspective view of a base plate 56 and itscylindrical hub portion 132 of the stator of the electric machine ofFIG. 53 , consistent with disclosed embodiments.

FIG. 57 illustrates a cross-sectional view of an electric machine cooledby a liquid-coolant in an axial plane, consistent with disclosedembodiments.

FIGS. 58-60 illustrate different views of the electric machine of FIG.57 , consistent with disclosed embodiments.

DETAILED DESCRIPTION

It should be noted that all relative terms such as “about,”“substantially,” “approximately,” etc. are used to indicate a possiblevariation of up to 15% (unless noted otherwise or another variation isspecified). For example, the cross-sectional area of a first regiondescribed in this disclosure as being substantially equal to, orsubstantially the same as, the cross-sectional area of a second regioncovers a variation in cross-sectional area of up to 15% in its ambit.Similarly, a dimension substantially equal “t” units (width, length,etc.) covers a variation of up to 15%. Additionally, a dimensiondescribed as being between a range (e.g., X-Y, X to Y, etc.) includesthe two boundaries. That is, a dimension between X-Y can be anydimension between X−15% to X+15%. Unless indicated otherwise, all termsrelating to the shape of an object or area refers to approximate shapes.For example, a cross-sectional shape described as being square(rectangular, trapezoidal, etc.) does not necessarily refer to an exactsquare (unless it is described as being such). Instead, slightvariations in the described shape (e.g., resulting from manufacturingprocesses, tolerances, etc.) are also covered. For example, the cornersof cross-sectional area described as being square may have rounded (orchamfered) corners, variations in corner angle of up to 15%, variationsin parallelism between the opposite sides of 15%, etc.

Unless defined otherwise, all terms of art, notations and otherscientific terms or terminology used herein have the same meaning as iscommonly understood by one of ordinary skill in the art to which thisdisclosure belongs. Some of the components, structures, and/or processesdescribed or referenced herein are well understood and commonly employedusing conventional methodology by those skilled in the art. Therefore,these components, structures, and processes will not be described indetail. All patents, applications, published applications and otherpublications referred to herein are incorporated by reference in theirentirety. If a definition or description set forth in this disclosure iscontrary to, or otherwise inconsistent with, a definition and/ordescription in these references, the definition and/or description setforth in this disclosure prevails over those in the references that areincorporated by reference. None of the references described orreferenced herein is admitted as prior art to the current disclosure.

Various embodiments of the current disclosure include a radial fluxelectric machine. As used herein, an electric machine (or electricalmachine) is a device that operates based on electromagnetic forces. Ingeneral, any type of electromechanical energy converter that operateson, or generates, electricity is an electric machine. Although notrequired, in some embodiments, the electric machine may be an electricmotor or an electric generator. During operation, an electric machinegenerates magnetic flux. In a radial flux electric machine, at leastsome portions of the generated magnetic flux extends perpendicular tothe axis of rotation of the machine. Electric machines include a statorand a rotor separated by an air gap. In a radial flux electric machine,the working (or main) magnetic flux may extend between the rotor and thestator through the air gap in the radial plane. FIG. 1 illustrates anexemplary radial flux electric machine 10 of the current disclosure.Internal details of electric machine 10 will be described with referenceto FIGS. 2 and 3 . Electric machine 10 illustrated in FIG. 1 may be anair-cooled system with a housing 50. External ribs 52 may be positionedon the surface of the housing 50 between an end shield 54 and a statorbase plate 56. As illustrated in FIG. 1 , the base plate 56 may includea plurality of pins 58 extending therefrom. The ribs 52 and pins 58 mayassist in transferring the heat generated by the electric machine 10during operation to the surrounding air. In the discussion below,electric machine 10 in the form of an electric motor will be described.However, the description is equally applicable to other types ofelectric machines, such as, for example, an electric generator. Whenelectric machine 10 operates, its shaft 20 rotates.

Electric machines of the current disclosure may include a rotorconfigured to rotate about an axis of rotation and a stator. As usedherein, a stator is any stationary or fixed part, component, or assembly(of components) of the electric machine, and the rotor is a part,component, or assembly that is configured to move with respect to thestator. In some embodiments, the rotor may be configured to rotate aboutan axis of rotation relative to the stator. The rotor is coupled to ashaft (rotor shaft) that rotates with the rotor. The axis about whichthe rotor (and the shaft) rotates is referred to as the “axis ofrotation.” FIG. 2 illustrates a cross-sectional view of electric machine10 (of FIG. 1 ) along an axial plane of the machine 10, and FIG. 3illustrates a cross-sectional view of machine 10 along a radial plane ofmachine 10. Axial plane refers to an imaginary plane that that the axisof rotation of the machine lies in (or is a part of). In other words,every point of the axis of rotation of the machine lines in the axialplane. In FIG. 2 , the axis of rotation 1000 of machine 10 lies in theaxial plane, and the axial plane bisects the machine 10 into twosymmetric halves. Radial plane refers to a plane that extendsperpendicular to the axis of rotation. The axis of rotation 1000 extendsperpendicular (e.g., into and out of the paper) to the radial plane.

In the discussion below, reference will be made to FIGS. 2 and 3 .Electric machine 10 includes a rotor 200 and a stator 100. The rotor 200is configured to rotate about the axis of rotation 1000 with respect tothe stator 100. The stator 100 includes a stator core 110 comprising aplurality of teeth 120, and the rotor 200 includes a rotor core 210comprising a plurality of permanent magnets 220. Electromagnetic coils300 are mounted on the teeth 120 of the stator 100. The rotor 200 isconnected to the shaft 20 that is configured to rotate about the axis ofrotation 1000. When electric power is provided to the coils 300, amagnetic field is generated. Based on the generated magnetic field,magnetic flux flows between the rotor 200 and the stator 100, therebyproviding a rotary force to the rotor. Electric machine 10 may be usedas a power source in any application. For example, in an electricvehicle, the electric machine 10 may drive the wheels of the electricvehicle.

In electric machines of the current disclosure, at least one of therotor and/or the stator may include a plurality of teeth annularlyarranged about the axis of rotation. As used herein, teeth refers toprojections that protrude from a body. The teeth may include a series ofsubstantially similar projections that protrude from the body. Forexample, in embodiments where the rotor includes teeth, a series ofsubstantially similar projections that protrude from a body or a core ofthe rotor comprise the teeth. And in embodiments where the statorincludes teeth, a series of substantially similar projections thatprotrude from a body or core of the stator comprise the teeth. In aradial flux electric machine, the teeth protrude in the radial plane. Inother words, the teeth line in the radial plane and protrude (inward oroutward) in the radial direction. Each projection forms a tooth.Typically, the projections (or teeth) are configured or shaped to directa substantial portion of the magnetic flux between the stator and therotor. With reference to FIGS. 2 and 3 , in electric machine 10, thestator 100 includes a plurality of teeth 120 arranged annularly andsymmetrically about the axis of rotation 1000 on a core 110 of thestator 100. As will be explained in more detail later, each tooth 120includes multiple pieces or parts that are arranged together to form acomposite or a multi-part tooth 120. The outline of three teeth 120 areshown using dashed lines in FIG. 3 . As will be described in more detaillater, each tooth 120 may have a trapezoidal cross-sectional shape inboth the axial plane (see FIG. 2 ) and the radial plane (see FIG. 3 ).

As can be seen in FIG. 3 , the rotor 200 is separated from the stator100 by an air gap 250. In some embodiments, as described previously,depending on the configuration of the rotor 200 and the stator 100,multiple air gaps may separate the rotor 200 and the stator 100. In theexemplary embodiment illustrated in FIGS. 2 and 3 , the stator 100includes nine teeth 120 and the rotor 200 includes ten permanent magnets220 (identified using dashed lines in FIG. 3 ). However, this is onlyexemplary. In general, any number of teeth 120 and permanent magnets 220may be provided. As best seen in FIG. 3 , each permanent magnet 220 mayinclude multiple permanent magnet segments 222 coupled together in theform of an arc about the axis of rotation 1000. Any number of segments222 may be included in each permanent magnet 220. In some embodiments,all permanent magnets 220 may include the same number of segments 222.In some embodiments, the multiple segments 222 may be attached together(e.g., by an adhesive material) to form a permanent magnet 220. Any typeof permanent magnet may be used. In some embodiments, the permanentmagnets 220 may include one or more of ferrites, alnico, samariumcobalt, or a neodymium alloy. In some embodiments, each permanent magnet220 may be coated with an electrically non-conductive material. In someembodiments, adjacent permanent magnets 220 may be separated from eachother by spacers 224. The spacers 224 may be made of an electricallynon-conductive material and may be attached to the adjacent permanentmagnets 220 by an adhesive material (e.g., glue). In some embodiments,the spacers 224 may be eliminated and adjacent permanent magnets 220 maybe separated from each other by a space or a gap.

The electric machines of the current disclosure may include a pluralityof electromagnetic coils. An electromagnetic coil (or an electric coil)may include one or more turns of an electrical conductor that generatesa magnetic field when an electric current is passed through theconductor (e.g., in electric motors), or generates a voltage across theconductor when a magnetic field passes over the coil. In someembodiments, the turns of electrical conductor may be configured orshaped like a coil, loop, twist, curl, or a spiral. In some embodiments,an electromagnetic coil may be an electrical conductor that contains aseries of conductive wires configured to be wrapped around aferromagnetic core. In general, electromagnetic coils of the currentdisclosure may be associated with the stator or the rotor of theelectric machine. That is, in some embodiments, the plurality of coilsmay be coupled to (e.g., mounted, installed, wound on, etc.) the rotorand in other embodiments, the plurality of coils may be coupled to thestator. In the exemplary embodiment of electric machine 10 illustratedin FIGS. 2 and 3 , a plurality of electromagnetic coils 300 are coupledto the stator 100. It should also be noted that the configuration of theelectric machine 10 illustrated in FIGS. 2 and 3 is only exemplary.

In the electric machine 10 of FIGS. 2 and 3 , a single rotor 200 ispositioned radially outwards a single stator 100. However, thisconfiguration is only exemplary, and electric machines of the currentdisclosure may have other configurations. FIGS. 8A-8E are schematicillustrations of exemplary configurations of electric machines of thecurrent disclosure showing the layout of the stator 100 relative to therotor 200. In each case, the rotor 200 is connected to a shaft 20 thatrotates about the axis of rotation 1000, and includes a plurality ofpermanent magnet segments 220 arranged annularly about the axis ofrotation 1000. And the stator includes a plurality of teeth 120 arrangedannularly about the axis of rotation 1000. Each tooth 120 comprisesmultiple parts and has a trapezoidal cross-sectional shape in both theaxial and radial planes (as in FIGS. 2, 3 ). And coils 300 are mountedon one or more of the teeth 120.

FIG. 8A schematically illustrates the electric machine 10 of FIGS. 2 and3 where the rotor 200 is positioned outside the stator 100. In such anembodiment, a width of each tooth 120 in the radial plane increases inthe radial direction (see FIG. 3 ) towards the air gap 250 (and therotor 200), and a length of each tooth 120 in an axial plane decreasesin the radial direction towards the air gap 250 (see FIG. 2 ). That is,with reference to FIGS. 2 and 3 , l₁>l₂ and w₁<w₂. In electric machine10A of FIG. 8B, the rotor 200 is positioned radially inwards of thestator 100. That is, in contrast with electric machine 10 of FIG. 8A,the rotor 200 of machine 10A is positioned closer to the axis ofrotation 1000 than its stator 100. FIG. 8C illustrates a cross-sectionalview of electric machine 10A (of FIG. 8B) in the radial plane. Inelectric machine 10A of FIGS. 8B and 8C, the width of the stator tooth120 in the radial plane (see FIG. 8C) decreases in a radially inwarddirection towards the rotor 200 and the air gap 250, and its length inthe axial plane (view illustrated in FIG. 8B) increases in the radiallyinward direction towards the rotor 200.

Electric machine 10B of FIG. 8D includes two stators 100A, 100Bpositioned on opposite sides of the rotor 200. Both the inner and theouter stator 100A, 100B include a plurality or multi-part teeth 120annularly arranged about the axis of rotation 1000. In electric machine10B, the width of each tooth 120 (in the radial plane) of the innerstator 100A increases in the radially outward direction toward the rotor200 (and air gap 250), and the width of each tooth 120 of the outerstator 100B decreases in the radially inward direction toward the rotor200 (and air gap 250). Conversely, as shown in FIG. 8D, the length ofeach tooth 120 (in the axial plane) of the inner stator 100A decreasesin the radially outward direction toward the rotor 200, and the lengthof the teeth 120 (in the axial plane) of the outer stator 100B increasesin the radially inward direction toward the rotor 200. In other words,if the width of a tooth 120 decreases in one direction its lengthincreases in that same direction, and vice versa.

Electric machine 10C of FIG. 8E includes two rotors 200A, 200Bpositioned on opposite sides of the stator 100. In such a configuration,the width of the stator tooth 120 (in the radial plane) increases in aradially outward direction towards the outer rotor 200B and decreases ina radially inward direction towards the inner rotor 200A. Conversely, asevident from FIG. 8E, the length of the stator tooth 120 (in the axialplane) decreases in a radial outward direction toward the outer rotor200B and increases in a radially inward direction toward the inner rotor200A. The cross-sectional area of each tooth 120 may increase in theradially outward direction. In electric machines 10-10C (of FIGS.8A-8E), a coil 300 is mounted on each tooth 120 such that it ispositioned close to the air gap 250 between the stator and the rotor.

FIG. 9 illustrates an exemplary electric machine 10F which includes aninner stator 100A and an outer stator 100B positioned on radiallyopposite sides of the rotor 200. Each of the inner and outer stators100A, 100B are separated from the rotor 200 by an air gap 250 (notvisible in FIG. 9 ). That is, electric machine 10F is a double air gapelectric machine. A coil 300 is mounted on the inner stator 100A. Unlikethe double stator electric machine 10B of FIG. 8D, in electric machine10F of FIG. 9 , a coil 300 is not mounted on the outer stator 100B.Instead, a coil 300 is only mounted on the teeth 120 of the inner stator100A.

FIG. 10 illustrates an exemplary double stator electrical machine 10Gwhich differs from an electrical machine 10F (of FIG. 9 ) in that theinner and outer stators 100A, 100B are connected by a magneticallyconducting bridge 140. Bridge 140 may be made of any suitable material,such as, for example, laminated steel, SMC, etc. SMC may provideisotropic magnetic properties (i.e., the ability to conduct magneticflux the same in all directions) to the bridge 140. It should be notedthat the configurations of electric machines discussed above are onlyexemplary. Many other variations are possible. Each of these variationsof electric machines include multi-part teeth 120 having a trapezoidalcross-sectional shape in the radial and axial planes with coils 300mounted on one or more teeth 120, as will be discussed in more detaillater.

FIGS. 11-22 are schematic illustrations of some exemplary variations ofradial flux electric machines of the current disclosure havingmulti-part teeth 120 with a trapezoidal cross-sectional shape in theradial and axial planes. In these figures, a cross-sectionalrepresentation of the electric machine in the axial plane is shown onthe left side and a cross-sectional representation of the electricmachine in the radial plane is shown on the right side. For the sake ofbrevity, only aspects of each electric machine that are different fromother described embodiments will be described below. In the electricmachine of FIG. 11 , the rotor 200 is mounted radially outside thestator 100. A plurality of multi-part teeth 120 are assembled andarranged in the form of a ring on the stator 100. Coils 300 extendaround each tooth 120. In the rotor 200, the permanent magnets 220 areannularly arranged in slots formed a drum 230 of the rotor 200 to forman air gap 250 between the stator 100 and the rotor 200.

In the electric machine of FIG. 12 , the rotor 200 is installed radiallybetween an inner and an outer stator 100A, 100B. The inner stator 100Ais made in the form of a ring and contains trapezoidal teeth 120. Aswill be explained later (with reference to FIGS. 23A-23K), in theelectric machines of FIGS. 11 and 12 , each tooth 120 is formed of acore tooth-portion 122 formed integrally with an annular part 130 of thestator core 110 and one or more additional wedge-shaped tooth-portions124A-124F assembled together to form a trapezoidal tooth 120. The rotor200 is configured to rotate between the inner and outer stators 100A,100B with air gaps 250 formed between each of the inner and outerstators 100A, 100B and the rotor 200. Electric machines with two airgaps (e.g., FIGS. 12, 13 , etc.) are referred to as double air gapelectric machines.

In the electric machine of FIG. 13 , as in the embodiment of FIG. 12 ,the rotor 200 is installed between the inner and outer stators 100A,100B, and the inner stator 100A is made in the form of a ring andincludes a plurality of multi-part teeth 120. The inner and outerstators 100A, 100B are connected by a magnetically conductive bridge140. The electric machine of FIG. 14 is similar to the electric machineof FIG. 11 , except that its teeth 120 are formed separate parts thatare assembled on the stator 100 (see, e.g., FIGS. 23L-23N, 24A-24D).That is, in the embodiment of FIG. 14 , as will be described withreference to FIGS. 23L-23N, each tooth 120 may be formed of multipleparts that are separate from the stator core 110.

FIG. 15 illustrates an electric machine where the rotor 200 is installedbetween inner and outer stators 100A, 100B, and the teeth 120 areseparate from the stator 100 (as explained with reference to FIG. 14 ).The electric machine of FIG. 16 is similar to the electric machine ofFIG. 15 except that a bridge 140 connects the inner and outer stators100A, 100B. In the electric machine of FIG. 17 , the rotor 200 isinstalled between inner and outer stators 100A, 100B that are connectedtogether by a bridge 140. The inner stator 100A includes multi-parttrapezoidal teeth 120 similar to that in the electric machine of FIG. 12, and the outer stator 100A is made of separate arc-shaped segmentsarranged in a ring. The electric machine of FIG. 18 is similar to theelectric machine of FIG. 17 except that its teeth 120 on the innerstator 100A are similar to that in the electric machine of FIG. 14 .

In electric machine of FIG. 19 , the rotor 200 is mounted inside thestator 100, and the stator teeth 120 are assembled on the outer stator100 made in the form of a ring. In the electric machine of FIG. 20 , therotor 200 is installed between the inner and outer stators 100A, 100Bthat are connected together by a bridge 140. The outer stator 100B, madein the form of a ring and includes teeth 120 with coils 300 mountedthereon. In the electric machine of FIG. 21 , the rotor 200 is installedbetween the inner and outer stators 100A, 100B. Both the inner and outerstators 100A, 100B are made in the form of rings and includestrapezoidal teeth 120 with coils 300 mounted thereon. The electricmachine of FIG. 22 is similar to the electric machine of FIG. 21 exceptthat the inner and outer stators 100A, 100B are connected by a bridge140.

The above described embodiments of electric machines are only exemplary.There may be many variations to the above-described embodiments. Since aperson skilled in the art would be able to recognize these variationsbased on the above disclosure, these variations are not discussedfurther herein. Furthermore, although the teeth 120 are described asbeing part of the stator 100 in the above described embodiments ofelectric machines, this is not a limitation. That is, in someembodiments, the teeth 120 may alternatively or additionally be part ofthe rotor 200. For the sake of brevity, in the discussion below,exemplary aspects of the current disclosure will be discussed withreference to the configuration of electric machine 10 illustrated inFIGS. 2 and 3 . It should be emphasized that this discussion appliesequally to other configurations of electric machines (such as, forexample, the configurations discussed above).

FIGS. 4A-4C illustrate different views of the stator 100 separated fromother components of electric machine 10 of FIGS. 2 and 3 . FIGS. 4A and4B illustrate perspective views of the stator 100, and FIG. 4Cillustrates a cross-sectional view of the stator 100 in the axial plane.Each coil 300 is mounted, or installed, on a tooth 120. In someembodiments, a coil may be installed on a tooth such that the innersurface of the coil 300 fits snugly against the outer surface of thetooth 120. In some such embodiments, the external shape (or profile) ofthe coil 300 may be substantially the same as the external shape of thetooth 120 that it is mounted on. FIG. 5 illustrates an electricalconnection diagram of an exemplary 3-phase winding 140 of electricalmachine 10. As best seen in FIGS. 4A-4B, each tooth 120 of stator 100 isseparated from an adjacent tooth 120 by a slot 160 that accommodates thecoils 300 mounted on the adjacent teeth 120. As illustrated in FIG. 5 ,the coils 300 mounted on the teeth 120 of the electric machine 10collectively form a 3-phase winding 310. It should be noted that,although the stator 100 is described as including teeth 120, in someembodiments, the rotor 200 may alternatively or additionally includeteeth 120.

FIGS. 6A-6D and 7A-7E illustrate different aspects of an electromagneticcoil 300 that may be mounted on a tooth 120. In the embodimentsillustrated in FIGS. 6A-6D, the coil 300 is made, or formed of, a foil312 of an electrically conductive material, and in the embodimentsillustrated in FIGS. 7A-7E, the coil 300 is made of an electricallyconductive wire 314. As would be recognized by a person skilled in theart, a foil is a strip of electrical conductor having a thickness and awidth. The width of the foil will typically be larger than itsthickness. That is, a foil is a thin strip of an electrically conductivematerial. In general, any type of an electrical conducting material maybe used to form the coil 300. In some embodiments, copper may be used.In some embodiments, the foil 312 may be coated with an electricallyinsulating material.

In the exemplary embodiments of coil 300 illustrated in FIGS. 6A and 6B,the coil 300 comprises multiple turns of foil 312 surrounding a centralcavity 320 that extends from a first end 322 to a second end 324 of thecoil 300. As illustrated in FIG. 6B, the coil 300 is mounted on a tooth120 such that the tooth 120 extends through the cavity 320. In someembodiments, as shown in FIGS. 6A and 6B, the width of the foil 312(i.e., the width along the flat side of the foil) may extend the entirewidth of a tooth 120 in the radial direction of the tooth (i.e., alongthe radial axis 2000). In some embodiments, as illustrated in FIGS. 6Cand 6D, a rib of foil 312 (i.e., a strip of foil 312 having a widthsmaller than the width of the tooth 120) may be wound, e.g., in the formof a spiral, in the radial direction along the tooth 120 to form a coil300 (see, e.g., FIGS. 6C, 6D).

In some embodiments, as illustrated in FIGS. 7A-7E, the coil 300 may bemade using one or more strands of an electrically conductive (e.g.,copper) wire 314. In some embodiments, the wire 314 may be coated withan electrically insulating material. In some embodiments, as shown inFIGS. 7A-7C, the wire 314 may be wound in the form of a spiral to definethe central cavity 320 of coil 300. The spirally wound wire 314 mayextend from the first end 322 to the second end 324 of the coil 300. Thewire 314 may have any cross-sectional shape. In some embodiments, asillustrated in FIG. 7D, the wire 314 may have a circular cross-sectionalshape. In some embodiments, as illustrated in FIG. 7E, the wire 314 mayhave a square or rectangular cross-sectional shape. It should be notedthat these illustrated cross-sectional shapes are only exemplary. Ingeneral, the wire 314 may have any cross-sectional shape. In someembodiments, to reduce eddy current losses, multiple wires 314 may betwisted together in the form of a Litz wire. As would be recognized by aperson skilled in the art, a Litz wire consists of multiple wirestrands, individually insulated, and twisted or woven together, arrangedin one of several patterns. These patterns may serve to equalize theproportion of the overall length over which each strand is at theoutside of the conductor. The use of stranded wires or Litz wire may bebeneficial to reduce eddy current losses and increase the efficiency ofthe electrical machine. An exemplary method of forming the coil 300using the foil 312 or the wire 314 will be described later withreference to FIGS. 45-47 .

In various embodiments, each coil of the disclosed electric machine mayhave a non-uniform trapezoidal cavity therethrough. Non-uniformtrapezoidal cavity refers to a cavity that has a non-uniformcross-sectional shape along a length portion thereof. In non-uniformcavity, a parameter related to a cross-sectional dimension of the cavityvaries over at least a portion of the length of the cavity. Anyparameter related to the dimension (e.g., width, height, length, area,perimeter, or another measure related to a dimension) may vary over(i.e., not be a constant over) a portion of the length of the cavity. Insome embodiments, in a non-uniform cavity, an area (or another measurerelated to dimension) of the cavity may not be uniform along a portionof the cavity length. In some embodiments, the area (or anotherdimensional measure) of the cavity may not be uniform over the entirelength (i.e., from one end of the cavity to the other end) of thecavity. In some embodiments, in a non-uniform cavity, one parameter(e.g., perimeter) may be uniform while another parameter (e.g., area)may be non-uniform over a portion of the cavity or the entire cavity.

As explained previously (with reference to FIGS. 6A-7E), whether made offoil 312 or wire 314, the coil 300 may include a cavity 320 that extendsfrom its first end 322 to second end 324. In various embodiments, cavity320 may be a non-uniform trapezoidal cavity. That is, a cross-sectionaldimension related parameter of the cavity may vary at least over aportion of the length between the first and second ends 322, 324. Withreference to FIG. 6B, coil 300 is mounted on a tooth 120 such that theinterior surfaces of its cavity 320 mates closely with, or is snugagainst, the exterior surfaces of the tooth 120. As a consequence ofsuch mounting, the internal shape of the cavity 320 of coil 300 may besubstantially the same as (or similar to) the external shape of thetooth 120. With reference to FIGS. 2 and 3 , the cross-sectional shapeof each tooth 120 in the radial and axial plane may be trapezoidal. Inother words, the tooth 120 may be trapezoidal shaped. The width andlength of each tooth 120 varies in the radial direction. That is, asillustrated in FIG. 2 , the length 13 of tooth 120 varies from l₁ to l₂in the radially outward direction of tooth 120 (along radial axis 2000),and as illustrated in FIG. 3 , the width w of tooth 120 varies from w₁to w₂ in the radially outward direction of tooth 120. As will beexplained later (with reference to 26A-26D), the perimeter of thecross-section of the tooth 120 in a plane perpendicular to the radialdirection may be substantially a constant in its radial direction whilethe area of the cross-section varies in the radial direction. In someembodiments, each tooth 120 may have a trapezoidal cross-sectional shapethat is non-uniform in the radial direction. The cavity 320 of coil 300may also have a similar trapezoidal cross-sectional shape that isnon-uniform in the radial direction.

In various embodiments, each cavity of the coil may be configured tocontain therein one tooth of the plurality of teeth. In general, thetooth may be contained or disposed in the coil cavity in any manner.That is, in some embodiments, each tooth may be snugly received in acoil cavity, while in other embodiments, the tooth may be looselyreceived in cavity. In some embodiments, portions of the externalsurface of the tooth may contact portions of the internal surface of thecavity that contains the tooth. In some embodiments, an interfacialmaterial may be disposed between the mating surfaces of the cavity andthe coil. With reference to FIG. 6B, in some embodiments, a tooth 120 issnugly contained in cavity 320 of coil 300 such that at least someportions of the outer surface of the tooth contact portions of the innersurface of the cavity 320. However, this is not required, and tooth 120may be contained in cavity 320 in any manner. That is, in someembodiments, the outer surface of tooth 120 in the cavity 320 may notmake physical contact with the inner surface of the cavity 320. In someembodiments, the outer surface of the tooth 120 and the inner surface ofthe cavity 320 may be separated by another material.

In various embodiments, each tooth may be formed of multiple piecesthat, when assembled together correspond to a shape of the non-uniformtrapezoidal cavity of the coil. As used herein, a piece refers to aportion or a part of the whole. A piece may have any size and shape. Thetooth may be formed of any number of pieces or parts and these multipleparts may have any shape and may be assembled together in any manner.For example, in some embodiments, the multiple parts may be glued orsecured together in another manner. In some embodiments, the multipleparts may be merely loosely or tightly placed together. In theembodiment of electric machine 10 of FIGS. 2 and 3 , the non-uniformtrapezoidal cavity 320 of the coil 300 is configured to contain themultiple parts that form a multi-piece tooth 120. The size and shape ofthe cavity 320 is configured to receive the multi-part tooth 120therein. In some embodiments, the size of cavity 320 of coil 300 may besubstantially the same as the size of tooth 120. In some embodiments,the cavity 320 may be sized slightly smaller than the tooth 120 suchthat, when the multi-part tooth 120 is assembled (as will be describedlater with reference to FIGS. 45-47 ), the coil 300 expands to snuglyreceive the tooth 120 in cavity 320.

FIGS. 23A-23K illustrate different exemplary embodiments of teeth 120 ofelectric machine 10 arranged on the core 110 of its stator 100. In theseembodiments, each tooth 120 includes multiple pieces or parts arrangedtogether to form the complete multi-part tooth 120. FIGS. 23A-23Dillustrate one exemplary embodiment of multi-part teeth 120, FIGS.23D-23H illustrate other exemplary embodiments of teeth 120, and FIGS.23I-23K illustrate further exemplary embodiments of multi-part teeth120. In should be noted that these illustrated embodiments are onlyexemplary and electric machines of the current disclosure may includeother types of multi-part teeth in the stator and/or the rotor.

FIG. 23A illustrates a perspective view and FIG. 23B illustrates anenlarged portion of FIG. 23A showing the structure of a single tooth120. FIGS. 23C and 23D illustrate cross-sectional views of FIG. 23A inthe radial and axial planes, respectively. Stator core 110 includes aring-shaped or annular part 130. Each multi-part tooth 120 of the stator100 extends in a radially outward direction from the annular part 130.When stator 100 and rotor 200 are assembled to form an electric machine10, each tooth 120 extends radially outwards towards the air gap 250(see FIGS. 2 and 3 ). As explained previously, tooth 120 has amulti-part construction. In the exemplary embodiment of tooth 120illustrated in FIGS. 23A-23D, each tooth 120 has a core tooth-portion122 and two additional tooth-portions 124A, 124B assembled together toform the tooth 120.

Core tooth-portion 122 is integral with the annular part 130 of statorcore 110, and each additional tooth-portion 124A, 124B is installed onan opposite side face of the core tooth-portion 122. The terms “integralwith” and “integrally formed,” are used to indicate that two parts areconnected to form a single part that practically cannot be dismantledwithout destroying the integrity of the part. In some cases, the twointegrally formed parts may be formed as a single part. In someembodiments, one or more of the additional tooth-portions may be shapedlike a wedge. As used herein, a wedge-shaped portion is part with anarrower end and a broader end. With reference to FIG. 23B, eachadditional tooth-portion 124A, 124B is a wedge-shaped component thatextends from a narrower first end 126 to a broader second end 128.Although the first and second additional tooth-portions 124A, 124B areillustrated as identical components in this embodiment, this is not arequirement.

FIGS. 23E-23H illustrate exemplary embodiments of tooth 120 having acore tooth-portion 122 and one additional tooth-portion 124C or 124Dthat are assembled to form the tooth 120. In these embodiments, the coretooth-portion 122 is integral with the annular part 130 of core 110, andthe additional tooth-portion 124C, 124D is wedge-shaped. The additionaltooth-portion 124C or 124D is installed on one side face of the coretooth-portion 122 to form the tooth 120. While the core-tooth portion122 (of the tooth 120) of FIGS. 23E (and 23A) extends radially outwardfrom the annular part 130 along the radial axis 2000, the coretooth-portion 122 of the tooth of FIG. 23G extends radially outwardsfrom its annular part 130 inclined at an angle γ with the radial axis2000. The core tooth-portion 122 may be inclined at any angle γ. In someembodiments, the angle of inclination γ will be similar to thatdescribed with reference to FIGS. 28A and 28B. It should be noted that,in some embodiments (e.g., the embodiment of FIG. 23E), the angle ofinclination γ may be zero. That is, the core tooth-portion 122 mayextend radially outward along the radial axis 2000 and a singleadditional tooth-portion may be installed on one side face of the coretooth-portion 122 to form the tooth 120. In the embodiment of FIGS.23I-23K, each tooth 120 has a core tooth-portion 122 and four additionaltooth-portions 112 a, 124A, 112 e, and 112 f that are assembled to formthe tooth 120. Core tooth-portion 122 is integral with the annular part130 of core 110, a first pair of additional tooth-portions 124A and 124Bare positioned on opposite side faces of the core tooth-portion 122, anda second pair of additional tooth portions 112 e and 112 f are arrangedon top and bottom faces of the core tooth-portion 12 a. It should benoted that the embodiments of tooth 120 discussed above are onlyexemplary, and the electric machines of the current disclosure mayinclude other configurations (e.g., having a different number and othershapes of additional tooth-portions) of tooth 120. It should also benoted that the illustrated shapes of the different parts (i.e., coretooth-portion and the additional tooth portion(s)) of tooth 120 are alsoexemplary. In general, the constituent parts of a tooth 120 may have anysuitable shape such that, when they are assembled, the external shape ofthe tooth 120 corresponds to the shape of the non-uniform trapezoidalcavity 320 of the coil 300.

In the embodiments of multi-part teeth described above with reference toFIGS. 23A-23K, one part (i.e., core tooth-portion 122) of each tooth 120is formed integral with the annular part 130 of the stator core 110 andat least one additional tooth-portion is formed separate from (i.e., notintegrated with) the core 110. However, such a configuration is notrequired. In some embodiments, all parts of the tooth may be separatefrom the stator core 110. These separate parts may be assembled to formthe tooth 120. FIGS. 23L and 23M illustrate exemplary embodiments of atooth 120 formed as separate components assembled on a hub 132 (see FIG.23N) to form the stator 100. In the embodiment of FIG. 23L, at its base134 the core tooth-portion 122 includes a rib 136 configured to beinserted into a correspondingly shaped groove in the hub 132 whenassembling the stator 100. In the embodiment of FIG. 23M, the base 134of the core tooth-portion 122 includes a groove 138 that fits on acorrespondingly shaped rib on the hub 132 when assembling the stator 100(see FIG. 24B). When all teeth 120 are assembled on the hub 132, thebases 134 of the teeth 120 may collectively form the annular part 130 ofthe stator 100 (see FIG. 24D).

FIGS. 24A-24D illustrate the installation of an exemplary tooth 120 (ofthe type illustrated in FIG. 23M) on the hub 132 to form the stator 100.As illustrated in FIG. 24A, the coil 300 is first mounted on themulti-part tooth 120. An exemplary method of mounting a coil 300 on atooth 120 is described later. As illustrated in FIG. 24B, the tooth 120with the coil 300 mounted thereon is installed on the hub 132 byinserting the groove 138 on the base 134 of the core tooth-portion 122into the correspondingly shaped rib on the hub 132. Additional teeth 120are then mounted on the hub 132 as illustrated in FIGS. 24C and 24D tocomplete the assembly of the stator 100.

In some embodiments, the multiple parts of the tooth 120 (coretooth-portion 122 and additional tooth portions 124A-124F) and the coil300 may be coupled together using an adhesive material (e.g., a hightemperature glue). In some embodiments, the adhesive material may befilled with a filler material (e.g., to impart desirable properties tothe adhesive). Any type of adhesive material may be used. In someembodiments, the coefficient of thermal expansion (CTE) of the adhesivematerial may be such that, when the tooth 120 heats up during operationof the electric machine, the thermo-mechanical stresses (induced due toCTE mismatch) induced in the tooth 120 and the coil 300 are withinacceptable limits (i.e., the stresses are below a value that may causefailure). In some embodiments, the CTE of the adhesive material may bewithin about 20% of the CTEs of the tooth components (e.g., steellaminations, SMC, etc.). In some embodiments, the CTE of the adhesivematerial may be within about 20% of the CTEs of the tooth components andthe coil 300.

In some embodiments, as illustrated in FIGS. 25A and 25B, a cage 142 (orcircumferentially wrapped bandage) may be installed on the stator 100.The cage 142 (or bandage) may assist in keeping the parts of the tooth120 (and/or coil 300) from protruding into the air gap 250 between thestator 100 and the rotor 200 (see FIG. 3 ) during operation. In someembodiments, windows may be provided on the surface of the cage 142 thefaces the rotor 200. In some embodiments, the cage 142 may also beattached to the teeth 120 using an adhesive material. In embodiments oftooth 120 where the core tooth-portion 122 is integral with the annularpart 130 of the stator core 110 (see, e.g., FIGS. 23A-23K), the coil 300and the additional tooth-portions 124A-124F are installed on the coretooth-portion 122 integrated with the core 110, as is described later.After all teeth 120 and the coils 300 are installed, in someembodiments, the cage 142 may be installed on the stator 100. The cage142 may be made of a non-magnetic material with low electricalconductivity or of a soft magnetic material with a relative magneticpermeability of greater than or equal to about 10 with low electricalconductivity. Making the cage 142 from a soft magnetic material resultsin suppression of high harmonics of the pulsating magnetic field, whichleads to a decrease in vibration and noise.

Because of the configurations of the core tooth-portion 122 and theadditional tooth-portion(s), each tooth 120 may have a trapezoidalcross-sectional shape in both the radial plane (see, e.g., FIGS. 3, 23C)and the axial plane (see, e.g., FIGS. 2, 23D). In some embodiments, asillustrated in FIG. 23B, the opposite side faces C and D of each tooth120 are not parallel to each other, and the opposite top and bottomfaces A and B of a tooth 120 are also not be parallel to each other(see, e.g., FIG. 23D). The opposite side faces C, D of adjacent teeth120 may however be parallel to each other such that the slot 160 formedbetween the adjacent teeth 120 has a constant width in the radialdirection (see, e.g., FIG. 23C). That is, side face C of one tooth 120may be parallel to side face D of the adjacent tooth 120.

In an embodiment where the rotor 200 is positioned outwards of thestator 100 (see FIGS. 2 and 3 ), the opposite side faces C and D of eachtooth 120 may diverge from each other in the radially outward direction(see, e.g., FIG. 23C), and the top and bottom faces A and B may convergetowards each other in the radially outward direction (see, e.g., FIG.23D). In an embodiment of an electric machine with an outer rotor 200and an inner stator 100 (FIGS. 2, 3 ) the width of each tooth 120 in theradial plane (FIG. 3 ) may increase in the radial direction (e.g.,increases from w₁ to w₂ in FIG. 3 ) towards the rotor 200, and a lengthof each tooth 120 in an axial plane (FIG. 2 ) may decrease in the radialdirection towards the rotor 200 (e.g., decreases from l₁ to l₂ in FIG. 2). The coil 300 may be mounted on each multi-part tooth 120 of thestator 100 with its inner surface snug against the outer surface of thetooth 120 (i.e., faces A, B, C, and D of FIGS. 23C and 23D) such thatthe outer surface of the coil 300 has substantially the same shape asthe underlying surface of the tooth 120. In some embodiments, the coil300 may be mounted on tooth 120 such that its radially outward end ispositioned close to the air gap 250 and the poles (of the permanentmagnets) of rotor 200 (see, e.g., FIG. 3 ). It should be noted thatalthough the discussion above makes specific reference to features(faces A, B, C, D, etc.) identified in the tooth 120 of FIGS. 23A-23D,the discussion above is equally applicable to all embodiments of tooth120 (in stator and/or rotor).

An electric machine 10 of the current disclosure may include a stator100 and a rotor 200 that is configured to rotate with respect to thestator 100 about an axis of rotation 1000. At least one of the stator100 or the rotor 200 may include a plurality of teeth 120 that areannularly arranged about the axis of rotation 1000. An electromagneticcoil 300 may be mounted on each tooth 120. Each coil 300 may have anon-uniform trapezoidal cavity 320, and each tooth 120 may be formed ofmultiple pieces. When the multiple pieces are assembled, the externalshape of the tooth 120 may correspond to the shape of the coil cavity320 that receives the tooth 120. In some embodiments, as will bedescribed later with reference to FIGS. 26A-26D, the external perimeterof each tooth 120 may correspond to an internal perimeter of the cavity320. In some embodiments, after a coil 300 is mounted on a multi-parttooth 120, the external perimeter of the tooth 120 may correspond to theinternal perimeter of the cavity 320 at each point in the radialdirection of the tooth 120.

In some embodiments, the multiple pieces of each tooth 120 may include acore tooth-portion 122 and at least one additional tooth-portion124A-124F (see, e.g., FIGS. 23A-23M). In some embodiments, each tooth120 may include a core tooth-portion 122 and two additionaltooth-portions 124A, 124B disposed on opposite sides of the coretooth-portion 122 (see, e.g., FIGS. 23A, 23K-23M). In some embodiments,the additional tooth-portions 1124A, 124B may be wedge-shaped. That is,these tooth-portions may extend from a narrower first end 126 to abroader second end 128.

In some embodiments, each tooth 120 may only include a coretooth-portion 122 and a single additional tooth portion 124C positionedon one side surface of the core tooth-portion 122 (see, e.g., FIG. 23H).In some embodiments, each tooth 120 a may include a core tooth-portion122 and a pair of wedge-shaped additional tooth-portions 124A, 124Bdisposed on opposite sides of the core tooth-portion 122 and anotherpair of additional tooth-portions 112 e, 112 f disposed on the top andbottom surfaces of the core tooth-portion 122 (see, e.g., FIG. 23K).Each additional tooth-portion of a pair may be substantially identical.In some embodiments, after a tooth 120 is assembled, in a planeperpendicular to the axis of rotation 100, the entire multi-part tooth120 may have a trapezoidal cross-sectional shape, the core tooth-portion122 (or tooth 120) may have a substantially rectangular cross-sectionalshape and each additional tooth-portion 124A, 124B, 124C may have asubstantially triangular cross-sectional shape (see, e.g., FIG. 23C,23H). And in a plane perpendicular to a radial direction, the multi-parttooth, the core tooth-portion 122, and the additional tooth-portions124A, 124B, 124C may each have a substantially rectangularcross-sectional shape (see, e.g., FIGS. 23A, 23F).

Regardless of how many parts a multi-part tooth 120 is made of, and thespecific shape of these parts, after a tooth 120 is assembled, across-section of each tooth 120 in the radial plane (see, e.g., FIGS. 3,23C, 23H) and the axial plane (see, e.g., FIGS. 2, 23D) may have atrapezoidal shape (and in some embodiments, an isosceles trapezoidalshape). In some embodiments, as will be explained later with referenceto FIGS. 26A-26D, the perimeter of the cross-section of a tooth 120 in aplane perpendicular to the radial direction of the tooth 120 issubstantially a constant in the radial direction, and the area of thecross-section varies in the radial direction. In an embodiment of theelectric machine with an inner stator 100 and an outer rotor 200 (see,FIGS. 2, 3 ), or an external stator 100 and internal rotor 200 (see,FIGS. 8B, 8C) the cross-sectional area increases in the radial directiontowards the rotor 200. In some embodiments, the cross-sectional area ofa tooth 120 in a plane perpendicular to the axis of rotation 1000 maydecrease in the axial direction from the center to the sides of thetooth 120 (see, e.g., FIGS. 27A-27D).

When the multiple pieces of each tooth 120 are assembled, each tooth 120may define external surfaces having two sets of opposing faces. Forexample, in the embodiment of tooth 120 illustrated in FIG. 23B,opposing side surfaces C and D form one set of opposing faces and theopposing top and bottom surfaces A and B form another set of opposingfaces. The opposing faces C, D (and A, B) of each set are non-parallelto each other. Each face of the two sets is inclined in the radialdirection of the tooth 120 (see FIGS. 23C, 23D). In some embodiments(e.g., in an embodiment with an outer rotor 200 and an inner stator100), the opposing faces (A, B) of one set may converge towards eachother in a radially outward direction (see, e.g., FIG. 23D) towards theair gap 250 (see FIG. 2 ), and the opposing faces (C, D) of the otherset may diverge from each other in the radially outward directiontowards air gap 250 (see FIGS. 3, 23C). In some embodiments (e.g., in anembodiment with an inner rotor 200 and an outer stator 100), the top andbottom opposing faces may diverge from each other towards the air gap250 (see FIG. 6B) and the opposing side faces may converge towards eachother towards air gap 250 (see FIG. 6C).

The different parts of tooth 120 (i.e., core tooth-portion andadditional tooth-portions) may be made of any suitable material (e.g.,steel laminations, Soft Magnetic Composite (SMC), etc.). In someembodiments, both the core tooth-portion 122 and the additionaltooth-portions 124A-124F of each tooth 120 may be made of the samematerial (e.g., SMC). In some embodiments, core tooth-portion 122 may bemade of a first material and the additional tooth-portions 124A-124F maybe made of a second material. For example, in some embodiments, the coretooth-portion 122 may be made of an SMC and the additional toothportions 124A-124F may be made from another isotropic material, forexample another SMC). This is due to the passage through coretooth-portion 122 and the additional tooth portions 124A-124F magneticflux, which changes in 3 directions and not in a plane. In embodimentswhere the core tooth-portion 122 is formed integrally with the annularpart 130 of the stator core 110 (see, e.g., FIGS. 23A, 23G), both thecore tooth-portion 122 and the annular part 130 may be made of the samematerial (e.g., SMC).

In various embodiments of the current disclosure, each tooth of theplurality of teeth of the electric machine extends in a radial directionsuch that a plurality of cross-sectional areas of each tooth in aplurality of planes perpendicular to the radial direction vary, andperimeters of the plurality of cross-sections are substantially the sameacross the plurality of perpendicular planes. Any direction that extendsperpendicular (or substantially perpendicular) to the axis of rotationof the electric machine is a radial direction of electrical machine. Forexample, in the embodiment illustrated in FIGS. 1 and 2 , any directionthat generally extends perpendicular to the axis or rotation 1000 is aradial direction. In some embodiments, the radial direction may extendalong, or be coincident with, a radial axis of the tooth of the electricmachine. As explained previously, in some embodiments, each tooth 120(of the stator 100 and/or the rotor 200) has a trapezoidalcross-sectional shape in both the radial plane (see FIG. 3 ) and theaxial plane (see FIG. 2 ), and the width of tooth 120 in the radialplane (see FIG. 3 ) increases in a radially outward direction (i.e.,towards the rotor 200), while the length of the tooth 120 in the axialplane (see FIG. 2 ) decreases in that same direction.

FIGS. 26A-26D are cross-sectional images of a tooth 120 along differentplanes. FIG. 26A illustrates the cross-sectional image of a single tooth120 in the axial plane (compare with FIG. 2 ). The tooth 120 is shownhatched in FIG. 26A. As evident from FIG. 26A, the cross-sectional shapeof tooth 120 in the axial plane is trapezoidal (i.e., a quadrilateralwith one pair of opposing parallel sides and another pair of opposingnon-parallel sides). In some embodiments, as will be explained withreference to FIGS. 31A and 31B, the cross-sectional shape of tooth 120in the axial and/or the radial planes is an isosceles trapezoid (i.e., atrapezoid where the length of the opposite sides are equal). As alsoevident from FIG. 26A, the length of tooth 120 decreases with increasingdistance in the radial direction, that in this embodiment, is coincidentwith the radial axis 2000. FIGS. 26B-26D illustrate cross-sections oftooth 120 at different planes (A-A, B-B, and C-C) perpendicular to theradial direction. FIG. 26B is the cross-sectional view of teeth 120along plane A-A, FIG. 26C is the cross-sectional view of teeth 120 alongplane B-B, and FIG. 26D is the cross-sectional view of teeth 120 alongplane C-C. As can be seen from FIGS. 26B-26D, in planes perpendicular tothe radial direction of the tooth 120, the tooth 120 has a rectangularcross-sectional shape.

In should be noted that, although, perfect rectangles with squarecorners (i.e., 90° corners) are illustrated in FIGS. 26B-26D, this isonly exemplary. As previously explained, in some embodiments, thesecross-sectional shapes may not be perfect rectangles. As would berecognized by a person skilled in the art, in some embodiments, theopposite sides of the rectangles may not be perfectly parallel, theadjacent sides may not be perfectly perpendicular, and the corners maybe rounded and/or chamfered. As illustrated in FIGS. 26B-26D, inembodiments of electric machines with an inner stator 100 and outerrotor 200 (see FIGS. 2-3 ), the rectangular shape gets shorter and wideras the distance in the radial direction increases. That is, as thedistance in the radial direction increases from the axis of rotation1000, the length of the tooth 120 decreases (i.e., a₁>b₁>c₁ anda₃>b₃>c₃), and the width of the tooth 120 increases (i.e., a₂<b₂<c₂ anda₄<b₄<c₄). Although not required, in some embodiments, the oppositesides of the cross-sectional shape may be equal. That is,(a₁=a₃)>(b₁=b₃)>(c₁=c₃), and (a₂=a₄)<(b₂=b₄)<(c₂=c₄). In other words,tooth 120 gets progressively shorter and wider in the radially outwarddirection from the axis of rotation 1000. The cross-sectional area oftooth 120 (i.e., the cross-sectional area in the plane perpendicular tothe radial direction) also varies in the radially outward direction. Inan embodiment where the rotor 200 is outside the stator 100 (e.g., FIGS.2, 3 ), the cross-sectional area may increase in the radially outwarddirection (i.e., S_(A)<S_(B)<S_(C)). In other embodiments of electricmachines, the area may vary in a different manner along the radialdirection. For example, in electric machines with an inner rotor andouter stator (see FIG. 8B-8C), the cross-sectional area may increase inthe radially inward direction.

With reference to FIGS. 26A-26D, the perimeter of each tooth 120 in theradial direction may be substantially a constant, while thecross-sectional area of each tooth 120 in the radial direction may vary.That is, the perimeter of the cross-sections of tooth 120 along planesA-A, B-B, and C-C (see FIGS. 26B-26D) may be substantially the same,while its cross-sectional area in these planes may not be a constant (ormay vary). That is, (a₁+a₂+a₃+a₄)≈(b₁+b₂+b₃+b₄)≈(c₁+c₂+c₃+c₄), and S_(A)S_(B) S_(C). Irrespective of the configuration of the electric machine,in all embodiments, the perimeter of each tooth (in a cross-sectionperpendicular to the radial direction) may remain substantially aconstant along the radial direction while its cross-sectional area mayvary in this direction.

FIGS. 27A-27D are cross-sectional views of a tooth 120 along differentplanes. Like FIG. 24A, FIG. 27A illustrates the cross-sectional image ofa tooth 120 in the axial plane. FIGS. 27B-27D illustrate cross-sectionsof tooth 120 at different planes (D-D, E-E, and F-F) perpendicular tothe axis of rotation 1000 (or parallel to the radial direction) alongthe axial direction of tooth 120 (i.e., along the axis of rotation1000). FIG. 27B is the cross-sectional view of tooth 120 along planeD-D, FIG. 27C is the cross-sectional view of tooth 120 along plane E-E,and FIG. 27D is the cross-sectional view of tooth 120 along plane F-F.As illustrated in these figures, in the axial direction from the middleto the end of the tooth 120, the cross-sectional area of the tooth 120decreases. That is, S_(D)>S_(E)>S_(F). In other words, thecross-sectional area of the tooth 120 in a plane perpendicular to radialdirection (and the radial axis 2000 in some embodiments) varies in theradial direction (see FIGS. 26B-26D), and the cross-sectional area ofthe tooth in a plane perpendicular to the axis of rotation 1000 (orparallel to the radial direction) varies in the axial direction (seeFIGS. 27B-27D). In an embodiment of electric machine 100 where the rotor200 is outside the stator 100 (FIGS. 2, 3 ), the cross-sectional area ofeach tooth 120 increases in the radial direction (see FIGS. 26B-26D) anddecreases in the axial direction (see FIGS. 27B-27D).

FIGS. 28A and 28B illustrate geometrical details of an exemplary tooth120 (of electric machine 10 of FIG. 2, 3 ). FIG. 28A is across-sectional view of the tooth 120 in the radial plane and FIG. 28Bis a perspective view of the tooth 120 (looking down on the tooth). Asexplained previously, in embodiments of an electric machine with aninner stator 100 and outer rotor 200, each tooth 120 becomes wider inthe radial plane as it extends radially outward (see FIG. 3 ). As shownin FIG. 28A, the opposite side surfaces C, D of tooth 120 forms an angleγ with the radial direction (and the radial axis 2000 in someembodiments) of the tooth 120. The value of angle γ may be determined bythe number of teeth 120 in electric machine 100. In general, angle 2γ(which is the angle between the opposite side surfaces C, D of tooth120) equals about 360 degrees divided by the number of teeth 120. Thatis, 2γ ≈360°/n, where n is the number of teeth. For example, for anelectric machine 10 with nine teeth 120 (see FIG. 3 ), the angle2γ≈360/9=40°. Thus, each side surface C, D of tooth 120 is inclined byabout 20° from the radial axis 2000. With reference to FIG. 28B, thefront and back surfaces of tooth 120 makes an angle β in the axial planeof the tooth 120. Angle β is also determined by the number of teeth ofthe electric machine (100). A tooth 120 having a substantially constantperimeter in the radial direction leads to the correlations (see FIG.28B): h₁=d₁; d₁=r*Sin(γ); h₁=r*Tan(β); r*Sin(γ)=r*Tan((3);Sin(γ)=Tan(β); β=Arctan(Sin(γ)), or β=1/Tan(Sin(γ)).

FIGS. 29A and 29B illustrate the cross-sectional view of an exemplarytooth 120 in the radial plane. Tooth 120 of FIG. 29B includes a polepiece or a shoe 112, while tooth 120 of FIG. 29A does not. As shown inthese figures, the width of tooth 120 increases in the radial direction(along radial axis 2000) (i.e., towards air gap 250, see FIGS. 2, 3 ).As explained with reference to FIGS. 26A-26D, the geometrical dimensionsof the tooth 120 are such that the cross-sectional area of the tooth 120increases in the radial direction. In both an embodiment of the tooth120 with a shoe 112 (FIG. 29B) and without (FIG. 29A), the increase incross-sectional area (S_(A)<S_(B)<S_(C)) along the radial direction maybe smooth. In some embodiments, the increase in cross-sectional area maybe monotonic. In some embodiments, the rate of variation (increase ordecrease) of the cross-sectional area may be a constant. A smoothvariation (increase or decrease) in cross-sectional area towards the airgap 250 enables the use of the radially outermost end 114 (or tip) ofthe tooth 120 and the shoe 112 (if a shoe is used) as a magneticconductor (or a magnetic field concentrator) even when a large currentis flowing through the coil 300 mounted on the tooth 120.

FIG. 30 is a schematic illustration of a tooth 120 and a portion of therotor 200 of the electric machine 10 of FIGS. 2 and 3 . As can be seenin FIG. 30 , the air gap 250 that exists between the stator 100 and therotor 200 is formed between the radially outermost end 114 of the tooth120 and the rotor 200 (the permanent magnets of the rotor). Asillustrated in FIG. 30 , in some embodiments, the coil 300 may bemounted on the tooth 120 such the radially outermost end 316 of the coil300 is positioned as close as possible to the air gap 250. The radialdistance y between the radially outermost end 316 of the coil 300 andthe radially outermost end 114 of the tooth 120 may depend on theapplication and fabrication methods used. In some embodiments, thedistance y may be less than or equal to about 20% of the air gap 250. Insome embodiments, the distance y may be between 0-20% of the air gap250. In some embodiments, the radially outermost end 316 of the coil 300may be substantially coincident with the radially outermost end 114 ofthe tooth 120 (i.e., y≈0). In other words, the radially outermost end316 of the coil 300 may not protrude beyond the radially outer-most end114 of the tooth 120.

As also illustrated in FIG. 30 , in some embodiments, the radiallyoutermost end 114 of the tooth 120 may be rounded or curved such thatthe radially outermost ends 114 of all the teeth 120 have asubstantially circular profile. The cross-sectional shape of the tooth120 in the axial plane and the radial plane may be an isoscelestrapezoid or non-isosceles trapezoid. FIGS. 31A and 31B are schematicillustrations (in the radial plane or the axial plane) of a tooth 120having an isosceles trapezoidal shape and a tooth 120A having anon-isosceles trapezoidal shape. It should be noted that the teeth of anelectric machine of the current disclosure may have an isosceles or anon-isosceles trapezoidal shape in the radial plane (see FIG. 3 ) and/orthe axial plane (see FIG. 2 ). The trapezoidal geometry of tooth 120, aswell as a smooth increase in the cross-sectional area of the tooth inthe radial direction and the location of the coil on the tooth close tothe gap may assist in reducing leakage fluxes of the electrical machinesand thereby assist in increasing its efficiency and power output.

As explained above, in some embodiments, the electric machines of thecurrent disclosure may include a stator 100 and a rotor 200 configuredto rotate with respect to the stator 100 about an axis of rotation 1000(see, e.g., FIGS. 2, 3, 8A-22 ). At least one of the stator 100 or therotor 200 may include a plurality of teeth 120 that are annularlyarranged about the axis of rotation 1000. The plurality of teeth 120 maybe annularly arranged on the stator 100 or on the rotor 200. Each tooth120 may extend in a radial direction such that the cross-sectional areas(e.g., S_(A), S_(B), S_(C)) of each tooth 120 in a plurality of planes(e.g., A-A, B-B, C-C) perpendicular to the radial direction varies (see,e.g., FIGS. 26A-26D). The perimeters of the plurality of cross-sectionsmay be substantially a constant across the plurality of perpendicularplanes. That is, the cross-sectional area of each tooth in a planeperpendicular to the radial direction may vary along the radialdirection while the perimeter of the cross-sections remainssubstantially a constant in this direction (see, e.g., FIGS. 26A-26D).

In some embodiments, the cross-sectional area of each tooth 120 in aplane perpendicular to the axis of rotation 1000 varies along the axialdirection (see, e.g., FIGS. 27A-27D). As explained previously, based onthe configuration of the rotor 200 and the stator 100, thecross-sectional area may increase or decrease towards the rotor 200 whena plurality of teeth are located on the stator. The cross-sectionalshape of each tooth 120 in both the radial plane and the axial plane maybe trapezoidal (see, e.g., FIGS. 2, 3, 6A-22 ). In some embodiments, thecross-sectional shape of each tooth 120 in the radial and/or axial planeis a non-isosceles trapezoid (see, e.g., FIG. 31A). While in someembodiments, the cross-sectional shape of each tooth 120 in the radialand/or axial plane is an isosceles trapezoid (see, e.g., FIG. 31B). Inembodiments where the rotor 200 is disposed radially outwards of thestator 100 (see, e.g., FIGS. 2, 3 ), a width of each tooth in a radialplane (see FIG. 3 ) increases in the radial direction towards the rotor200, and a length of each tooth in an axial plane (see FIG. 2 )decreases in the radial direction towards the rotor 200.

As explained previously, the electric machine may also include aplurality of electromagnetic coils 300. The method of forming a coil 300is described later with reference to FIGS. 48-52 . Each coil 300 may bemounted on, and extend around, a separate tooth 120 of the electricmachine (see, e.g., FIGS. 8A-22 ). The method of mounting a coil 300 ona multi-part tooth 120 is described later with reference to FIGS. 45-47. Each coil 300 may include an electrical conductor (e.g., copper wire)in the form of a wire 314 having any cross-sectional shape or a flatfoil 312. In some embodiments, the wire 314 may have one of a square,rectangular, or circular cross-sectional shape (see, e.g., FIGS. 7D,7E). Any type of wire 314 may be used to form the coil 300. The wire mayinclude a single strand or multiple strands (e.g., twisted together). Insome embodiments, the wire may be a multi-strand wire (see, e.g., FIGS.7A, 7B). In some embodiments, each coil 300 may be wound in the form ofa spiral in the radial direction along a tooth 120 (see, e.g., FIG. 7B).In some embodiments, in place of a wire, a foil 312 (e.g., a copperfoil) may be used to form the coil 300 (see, e.g., FIGS. 6A-6D). Thefoil 312 may be wound around a tooth 120 such that a width of the foilextends over the entire length of the tooth 120 in the radial direction(see, e.g., FIG. 6A). Alternatively, in some embodiments, a thinner foil(e.g., a foil having a width less than the length of the tooth 120 inthe radial direction) may be wound (e.g., on a rib) in the form of aspiral in the radial direction along the tooth 120 (see, e.g., FIGS. 6C,6D).

As explained previously, teeth 120 may include multiple parts (coretooth-portion 122 and one or more additional tooth-portions 124A-124F)coupled together (see, e.g., FIGS. 23A-23M). As also explainedpreviously, these multiple parts may be made of the same material or ofdifferent materials (SMC, etc.). In some embodiments, the coretooth-portion 122 may be integrally formed with an annular ring 130 ofthe stator core 110 that extends around the axis of rotation 1000. Insome embodiments, one or more of the additional tooth-portions (e.g.,124A, 124B, 124E, 124F) may be wedge-shaped and disposed on oppositesides of the core tooth-portion 122. Each tooth 120 extends in theradial direction such that the cross-sectional area of the tooth 120 ina plane perpendicular to the radial direction may vary in the radialdirection toward the rotor. In embodiments where the rotor 200 ispositioned radially outwards of the stator 100, the cross-sectional areaof the tooth 120 increases in the radial direction towards the rotor200.

In various embodiments of electric machines of the current disclosure,the stator may include an annular stator ring extending about the axisof ROTATION. As used herein, an annular stator ring is a ring-shapedstructure associated with the stator. The ring-shaped structure may bedisposed about the axis of rotation of the electric machine. Withreference to FIGS. 23A-23K, for example, stator 100 of electric machine10 includes an annular part 130 that extends around the axis of rotation1000. Various embodiments of the electric machines of the currentdisclosure may also include a plurality of multi-part teethcircumferentially arranged on the stator ring. In other words, theplurality of teeth may each include multiple parts and they may bepositioned on or near the circumference of the annular stator ring. Asbest seen in FIGS. 23A and 23C, in embodiments of the currentdisclosure, a plurality of multi-part teeth 120 are circumferentiallyarranged on the annular part 130 of stator 100.

In various embodiments, each multi-part tooth of the plurality ofmulti-part teeth may include a core tooth-portion integrally formed withthe stator ring and at least one additional tooth-portion separate fromthe stator ring. That is, the core tooth-portion may be connected to thestator ring such that they form a single component and the at least oneadditional tooth-portion forms one or more additional components. Insome embodiments, core tooth-portion and the stator ring may be formedas a single part and the additional tooth-portion(s) may be formed asseparate parts. In some embodiments, the core tooth-portion and thestator ring may be formed as separate parts but may be attached together(e.g., fused or otherwise irremovably attached) to form a single partthat may not be easily disassembled without destroying the integrity ofthe part, while the additional tooth-portion(s) may be attached togetherin a way that they may be easily separated from the stator ring.

As explained previously with reference to FIGS. 23A-23M, each tooth 120of electric machine 10 may include multiple parts (e.g., coretooth-portion 122 and additional tooth-portions 124A-124F) arrangedtogether. In the exemplary embodiments of the tooth 120 discussed withreference to FIGS. 23A-23K, the core-tooth portion 122 of each tooth 120is integrally formed with the annular part 130 (of the stator core 110)that extends around the axis of rotation 1000, and one or moreadditional tooth-portions 124-124K positioned on the side surfacesand/or the top and bottom surfaces of the core tooth-portion 120 to formthe tooth 120.

FIG. 32A illustrates an exemplary embodiment of the annular part 130 ofthe stator core 110 with a plurality of core tooth-portions 122 arrangedannularly on the annular part 130. Each core tooth-portion 122 extendsradially outwards from the annular part 130 and includes a part of amulti-part tooth 112 (see FIG. 23A). In the embodiment of annular part130 illustrated in FIG. 32A, each core tooth-portion 122 extendsradially outwards from the annular part 130 along the radial axis 2000.However, as explained with reference to FIG. 23G, this is not arequirement. That is, in some embodiments, the core tooth-portion 122may extend radially outwards from the annular part 130 but may beinclined with respect to the radial axis 2000.

The stator core 110 that forms the annular part 130 may be formed as asingle part (i.e., not multiple parts that are joined together) asillustrated in FIG. 32A. In some embodiments (e.g., when the stator core110 is made of SMC or another brittle material), fabricating a statorcore 110 as a single part may be difficult and/or expensive. Duringfabrication of the stator core 110 and the operation of the electricmachine, the parts of the core 110 may experience significant stresses(e.g., compression during fabrication, alternating pulsating loads, andthermo-mechanical forces, etc. during operation, etc.). These largestresses may limit the size of the stator core 110 that may befabricated as a single part. For example, in some embodiments, the ratioof the thickness (e.g., thickness of the core-tooth portion 122) to theaxial length (i.e., the height along the axis of rotation 1000) of thestator core 110 that may be reliably fabricated as a single part may beless than or equal to about 1:6. Larger sized stator cores 110 may befabricated as multiple parts in some embodiments.

As illustrated in FIGS. 32B-32E, a stator core 110 may be made ofmultiple parts and then attached together. FIGS. 32B and 32C illustratean exemplary stator core 110 made of two mirror-symmetric halves 110A,110B that are attached together along the plane of symmetry to form thestator core 110. As illustrated in these figures, each half of the core110A, 110B includes a half 122A, 122B of the core tooth-portion 122. Thetwo halves 110A, 110B may be attached together using any type ofadhesive material. In some embodiments, a permanent adhesive (e.g., anadhesive that cannot be removed easily without destroying the integrityof the part) may be used to attach the two halves 110A, 110B of the core110 together. The CTE of the adhesive material used to attach the twohalves 110A, 110B of the core 110 may within about 20% of the CTE of thematerial that forms the core 110 to reduce CTE mismatch inducedthermo-mechanical stresses. In general, the stator core 110 may beformed by any number of parts that are joined together. FIGS. 32D and32E illustrate an exemplary stator core 110 made of three parts 110A,110B, 110C that are joined together (e.g., using the adhesive materialdiscussed above).

To increase the strength of the stator 100, one or more parts of thestator core 110 may be made of laminated electric steel sheets assembledtogether. In some embodiments, multiple laminated steel sheets (e.g.,silica-steel sheets) between, e.g., about 0.014″ to 0.018″ (29 to 26gauge) thick and coated with a very thin layer of insulation (e.g.,about 0.001″ thick insulation layer) may be attached together to form alaminated steel part of the stator. In some such embodiments, amulti-part tooth 120 of the type described with reference to FIG. 23Kmay be used. The annular part 130 and the core tooth-portion 122 can bemade of laminated steel or an isotropic material (SMC), and theadditional portions 124A-124F may be made of isotropic material such asSMC. Due to the three-dimensionality of the magnetic fields, using apair of additional tooth-portions 124A, 124B on the opposite sidesurfaces of the core tooth-portion 122 and another pair of additionaltooth-portions 124E, 124F on the opposite top and bottom surfaces of thecore tooth-portion 122 may provide suitable magnetic performance.

FIGS. 33A-33C illustrate an exemplary stator core 110 made of multiplematerials. With reference to these figures, the stator core 110 includesupper and lower annular parts 130A, 130C attached to a central annularpart 130B to form the annular part 130 of core 111. As shown in FIG.33C, the upper and lower annular parts 130A, 130C may be identicalcomponents. In general, annular parts 1300A, 130B, and 130C may be madeof any material (e.g., SMC, laminated steel, etc.) The upper and lowerannular parts 130A, 130C may be made by attaching rings made oflaminated steel together. The central annular part 130B may be made ofSMC. In some embodiments, as best seen in FIG. 33B, core tooth-portion122 may extend radially outwards from the central annular part 130B, andthe upper and lower additional tooth-portions 124E and 124F may beattached to the upper and lower annular parts 130A, 130C and the top andbottom surfaces of the core-tooth portion 122 The additional toothedportions 124A, 124B, 124E, and 124F may be made of an isotropic material(SMC), and the upper and lower annular portions 130A, 130C, the centralannular portion 130B, and the core tooth portion 122 may be made oflaminated steel or isotropic material (SMC).

In various embodiments of the current disclosure, each coil of theplurality of electromagnetic coils is mounted on a different multi-parttooth of the plurality of multi-part teeth such that each coil surroundsa corresponding core tooth-portion of the multi-part tooth with a gapbetween the coil and the core tooth-portion, and the at least oneadditional tooth-portion is disposed in the gap. Each multi-part toothmay be associated with a separate electromagnetic coil. The coil mayextend around the core-tooth portion of that multi-part tooth such oneor more spaces or gaps are formed between the coil and the coretooth-portion. And the additional tooth-portions are positioned in thesespaces or gaps. In some embodiments, as illustrated (for example) inFIGS. 4A, 23F, 23H, 23J, 23K, the core tooth-portion 124 of eachmulti-part tooth 120 is mounted on a coil 300 such that the coil 300extends around the core tooth-portion 124 with one or more gaps formedbetween the outer surfaces of the core tooth-portion 124 and the innersurface of the coil 300. In the embodiment of FIG. 4 and FIG. 23A, wherethe multi-part tooth 120 is formed of a core tooth-portion 122 and apair of additional tooth-portions 124A, 124B positioned on opposite sidesurfaces of the core tooth-portion 122, two gaps are formed between theopposite side surfaces of the core tooth-portion 124 and the innersurface of the coil 300 when the coil 300 is mounted on the coretooth-portion 122. One of the additional tooth-portions 124A, 124B ispositioned in one gap and the other additional tooth-portion 124B ispositioned in the other gap. In the embodiment of FIG. 23F where themulti-part tooth 120 is formed of a core tooth-portion 122 and a singleadditional tooth-portion 124C, this additional tooth-portion 124C ispositioned in the gap formed between the side surface of the coretooth-portion 122 and the coil 300. And, in the embodiment of FIG. 23K,four gaps are formed between the external surfaces of the coretooth-portion 122 and the inner surface of the coil 300, and eachaddition tooth-portion 124A, 124B, 124E, 124F is positioned in aseparate gap.

In some embodiments, electric machines (electric motor or generator) ofthe current disclosure may include a stator 100 and a rotor 200configured to rotate with respect to the stator 100 about an axis ofrotation 1000 (see, e.g., FIGS. 2, 3, 8A-22 ). At least one of thestator 100 or the rotor 200 may include a plurality of multi-part teeth120 that are arranged about the axis of rotation 1000. The stator 100may include an annular stator ring or part 130 extending about the axisof rotation 1000 (see, e.g., 23A, 23G, 23K, etc.). In some embodiments,the plurality of multi-part teeth 120 may be circumferentially arrangedon the stator ring 130. Each multi-part tooth 120 may include a coretooth-portion 122 integrally formed with the stator ring 130 and atleast one additional tooth-portion (e.g., additional tooth-portions124A, 124B, 124E, 124F) formed separate from the stator ring 130. Theelectric machine may also include a plurality of electromagnetic coils300. And each coil 300 may be mounted on a separate tooth 120 such thatthe coil 300 surrounds the core tooth-portion 122 of the multi-parttooth 120 with gap(s) formed between the coil 300 and the coretooth-portion 122 (see, e.g., 23E-23F, 23I-23K, 24A, etc.), and theadditional tooth-portion may be disposed in the gap(s).

In some embodiments, the annular part (or ring) 130 may be formed ofSMC. In some embodiments, the annular part 130 may be formed oflaminated steel. In some embodiments, one portion of the annular part130 may be formed of one material (e.g., laminated steel) while anotherportion is made of another material. In some embodiments, the annularpart 130 may be formed as a single part (see, e.g., FIG. 32A). In otherembodiments, the annular part 130 may be made of multiple parts (see,e.g., FIGS. 32B-32E). In some embodiments, the annular part 130 of thestator 100 may include two minor-symmetric halves coupled together alonga plane of symmetry perpendicular to the axis of rotation 1000 (see,e.g., 32B-32C). The annular part 130 may include two or moresubstantially identical parts attached together (see, e.g., FIG.32B-32E). Any type of adhesive material may be used to attach the partsof the stator ring 114 together. The CTE of the adhesive material may bewithin about 20% of the CTE of the attached components.

The annular stator ring 130 may include multiple (two, three, four,etc.) axially stacked annular parts (see, e.g., FIGS. 32B-33C). In someembodiments, each of the stacked annular parts may be made of the samematerial (e.g., SMC, laminated steel), while in other embodiments, thestacked annular parts may be made of different materials. For example,with reference to the annular part 130 of FIG. 33B, the top and bottomannular parts 130A, 130C may be made of one of laminated steel or SMC,and the central annular part 130B may be made of the other of laminatedsteel or SMC.

The core tooth-portion 122 of each multi-part tooth 120 may extendoutward in a radial direction from the annular stator ring 114 (see,e.g., FIGS. 23C, 23G). In some embodiments, the core tooth-portion 122extends radially outward from the annular stator ring 130 along theradial axis 2000 of the stator ring 130 (see, e.g., FIG. 23C). In someembodiments, the core tooth-portion 122 extends radially outward fromthe annular stator ring 130 inclined from the radial axis 2000 (see,e.g., FIG. 23G).

A cross-section of each of the core tooth-portion 122 and the at leastone additional tooth-portion 124A-124F along a plane perpendicular tothe radial direction has a substantially rectangular shape (see, e.g.,FIG. 23A, 23F, 23K). In some embodiments, a cross-section of the coretooth-portion 112 a along a plane perpendicular to the axis of rotationhas a substantially rectangular shape and a cross-section of the atleast one additional tooth-portion along the plane perpendicular to theaxis of rotation has a substantially triangular shape (see, e.g., FIGS.23C, 23H). In some embodiments, a cross-section of each multi-part tooth120 in the radial plane has a trapezoidal shape (see, e.g., FIGS. 3,23C, 23H). In some embodiments, the cross-sectional shape of eachmulti-part tooth 112 in the axial plane is also trapezoidal (see, e.g.,FIGS. 2, 23D). In some embodiments, the cross-sectional shape of thetooth 120 in the radial and/or the axial plate is an isosceles trapezoid(see, e.g., FIGS. 31A, 31B). In some embodiments, the perimeter of thecross-sectional area of each multi-part tooth 120 in a planeperpendicular to the radial direction of the tooth is substantially aconstant in the radial direction while the area of the cross-sectionalare varies in the radial direction (see, e.g., FIGS. 26A-26D). Eachtooth 120 may include a pair of additional tooth-portions 124A, 124B,124E, 124F arranged symmetrically on opposite sides of the coretooth-portion 124 (see, e.g., FIGS. 23C, 23K). In some embodiments, eachtooth 120 includes a first pair of additional tooth-portions 124A, 124Barranged symmetrically on a first pair of opposite sides (e.g., oppositeside surfaces) of the core tooth-portion 122 and a second pair ofadditional tooth-portions 124E, 124F arranged symmetrically on a secondpair of opposite sides (e.g., top and bottom surfaces) of the coretooth-portion 122 (see, e.g., FIG. 23K).

The core tooth-portion 122 and the additional tooth-portions of eachmulti-part tooth 120 may be coupled together using an adhesive material.In some embodiments, the multiple parts of the mule-part tooth 120 andthe coil 300 may be attached together by the adhesive material. Anysuitable type of adhesive material (e.g., glue) may be used. In someembodiments, the adhesive material may include a filler material tomodify the properties of the adhesive material. In some embodiments, theCTE of the adhesive material may be within about 20% of the CTE of thematerials of the tooth 120. In some embodiments, the CTE of the adhesivematerial may be within about 20% of the CTE of the materials of thetooth 120 and the coil 300.

At least one additional tooth-portion of each multi-part tooth 120 maybe wedged between an internal surface of the coil 300 and an externalsurface of the core tooth-portion 122 (see, e.g., FIGS. 23F, 23K, 24A).In some embodiments, the coil 300 surrounds the core tooth-portion 122of each tooth 120 such that at least two gaps are formed between aninner surface of the coil 300 and opposite sides of the coretooth-portion 122, and each additional tooth-portion is disposed in adifferent gap (see, e.g., FIGS. 23K, 24A). In some embodiments, eachtooth 120 includes a single wedge-shaped additional tooth-portiondisposed in a gap between the coil 300 and the core tooth-portion 122(see, e.g., FIG. 23F).

Various embodiments of the electric machines of the current disclosuremay include a stator having an annular stator ring and a plurality ofcore tooth-portions extending in a radial direction. As used herein, anannular stator ring is a ring-shaped component of the stator. Further,teeth are a series of projections that protrude from the annular statorring. Each projection form a tooth. Core tooth-portion is a portion ofthe tooth that is attached to the stator core. As explained previously,with reference to FIGS. 23A-23K and 32A-32E, in some embodiments, stator100 of electric machine 10 includes a stator core 110 with an annularpart 130 that extends around the axis of rotation 1000. As can also beseen in these figures, a core tooth-portion 124 extends in a radialdirection from the annular part 130 of the stator core 110. The coretooth-portion 124 forms a part of the multi-part teeth 120 of the stator100.

In various embodiments, the annular stator ring and the plurality ofcore tooth-portions are integrally formed of a Soft Magnetic Composite(SMC). As used herein, the term “integrally formed” indicates that thestator ring and the core tooth-portion are connected to form a singlepart that practically cannot be dismantled without destroying theintegrity of the part. In some cases, the stator ring and the coretooth-portion are formed as a single part. In some embodiments, the coretooth-portion and the stator ring may be formed as separate parts butmay be attached together (e.g., fused or otherwise irremovably attached)to form a single part that may not be easily disassembled withoutdestroying the integrity of the part. Soft magnetic composites (SMC) mayinclude ferromagnetic powder particles, which in some embodiments, arecoated with a layer of electrical insulating film. In some embodiments,the SMCs may include ferromagnetic powder particles surrounded by anelectrical insulating film. The components made of SMC may bemanufactured by conventional powder metal compaction techniques. In somecase, an integrally formed SMC stator core may offer several advantagesover traditional laminated steel cores. For example, these stator coresmay exhibit one or more of three-dimensional (3D) isotropicferromagnetic behavior, very low eddy current losses, relatively lowtotal core loss at medium and high frequencies, improved thermalcharacteristics, and a reduced weight. Any now-known or later-developedSMC may be used in embodiments of the current disclosure. In someembodiments, a commercially available SMC (e.g., Sintex® SMC, Somaloy130i, Somaloy 500, Somaloy 700 IP, Somaloy 700 3P, Somaloy 700 5P, oranother suitable SMC) may be used.

As explained previously with reference to FIGS. 23A-23M, each tooth 120of electric machine 10 includes multiple parts (e.g., core tooth-portion122 and additional tooth-portions 124A-124F) arranged together. In theexemplary embodiments of the tooth 120 discussed with reference to FIGS.23A-23K (and FIGS. 32A-32E), the core-tooth portion 122 of each tooth120 that extends radially outward from the annular part 130 of thestator core 110 is integrally formed with the annular part 130. One ormore additional tooth-portions 124-124K are positioned on the sidesurfaces and/or the top and bottom surfaces of the core tooth-portion122 to form the multi-part tooth 120. In the embodiment of tooth 120illustrated in FIG. 23A (and FIGS. 21A-32E), each core tooth-portion 124extends in a radial direction outwards from the annular part 130 alongthe radial axis 2000 of a tooth 120. However, as explained withreference to FIG. 23G, this is not a requirement. That is, in someembodiments, the core tooth-portion 122 may extend radially outwardsfrom the annular part 130 inclined with respect to the radial axis 2000.

The integrally formed core tooth-portion 122 (of a tooth 120) and theannular part 130 may be made of the same material. In some embodiments,the integrally formed annular part 130 and core tooth-portion 122 may beformed of an SMC. The additional tooth-portions 124A-124F that areassembled with the core tooth-portion 122 to form a complete tooth 120may be formed of SMC or another isotropic material ( ). In someembodiments, both the core tooth-portion 122 and the additionaltooth-portions 124A-124F may be formed of SMC. In some embodiments, thecore tooth-portion 122 (and annular part 130) may be made of SMC It isalso contemplated that, in some embodiments, the core tooth-portion 122(and annular part 130) may be made of steel laminations while some orall of the additional tooth-portions 124A-124F are formed of SMC.

In some embodiments, as described with reference to FIGS. 33A-33C, thestator core 110 may include upper and lower annular parts 130A, 130Cattached to a central annular part 130B to form the annular part 130 ofcore 110. In some such embodiments, as best seen in FIG. 33B, the coretooth-portion 122 may be integrally formed with the central annular part130B and extend outward in a radial direction from the central annularpart 130B. In general, annular parts 130A, 130B, and 130C may be made ofany material (e.g., SMC, laminated steel, etc.). In some embodiments,the central annular part 130B and the core tooth-portion 122 may beformed of SMC and the upper and lower annular parts 130A, 130C may withlaminated steel.

As explained previously, any suitable SMC may be used to fashion theintegrally formed annular stator ring 130 and the plurality of coretooth-portions 122. In various embodiments of the current disclosure,the SMC may include one or more isotropic ferromagnetic materials, amagnetic saturation induction of at least 1.6 Tesla, and an electricalresistivity over 10 micro-ohm/m. A ferromagnetic material is a substancethat conducts a magnetic field well. Examples of ferromagnetic materialsinclude iron, cobalt, nickel, gadolinium, chromium dioxide (CrO₂), andothers. In some embodiments of the current disclosure, the ferromagneticmaterial may be an iron-based material. An isotropic material has one ormore properties that are the same value in different directions. Anyproperty of the material may be the same in different directions. Insome embodiments, one or more magnetic properties of the isotropicferromagnetic material may be the same in different directions. In someembodiments, the magnetic saturation induction and/or the electricalresistivity of the material may be the same in all directions. Magneticsaturation induction is an indicator or how much magnetism can beinduced in a material or a component made of the material. Because ofmagnetic saturation, there is a point of diminishing returns beyondwhich applying an increased magnetic field will give rise to minimaladditional magnetic induction. Magnetic saturation inductioncharacterizes the saturation of the soft magnetic material to a state inwhich the induction does not increase with a further increase in themagnetic field strength. Electrical resistivity is a fundamentalproperty of a material that indicates how strongly the material resistselectric current. It is the inverse of electrical conductivity thatquantifies how well a material conducts electricity. A low value ofelectrical resistivity indicates that a material readily allows electriccurrent to pass through.

In some embodiments, the SMC material used to fashion the integrallyformed annular stator ring 130 and the plurality of core tooth-portions122 may be an isotropic ferromagnetic material having a magneticsaturation induction greater than or equal to (≥) about 1.6 Tesla and anelectrical resistivity greater than about 10 micro-ohm/m. In someembodiments, the SMC may have a magnetic saturation induction ≥about 2.4Tesla. In some embodiments, the magnetic saturation induction of the SMCmay be ≥about 2.5 Tesla. In some embodiments, the magnetic saturationinduction of the SMC may be between about 2.4-2.6 Tesla. The electricalresistivity of the SMC may be ≥about 10 micro-ohm/m (μΩ/m). In someembodiments, the electrical resistivity of the SMC may be ≥about 100μΩ/m (≥about 150 μΩ/m, ≥about 300 μΩ/m, ≥about 400 μΩ/m, or ≥about 500μΩ/m). In some embodiments, the electrical resistivity of the SMC may bewithin about 10-600 μΩ/m. The isotropy of the properties of the SMC mayassist in generating a three-dimensional magnetic field in the volume ofthe tooth 120. A magnetic saturation induction ≥about 1.6 Tesla of theSMC may help to maintain the properties of a magnetic conductor or amagnetic field concentrator and, accordingly, reduce leakage fluxes andincrease torque values and the power of the electric machine 10.Electrical resistivity of the SMC ≥about 100 μΩ/m may assist in reducingeddy current losses at a wide range of speeds and frequencies ofoperation of the electric machine 10. Thus, fashioning the integrallyformed annular stator ring 130 and the plurality of core tooth-portions122 of an SMC may result in an increase in the efficiency of electricmachine by increasing the magnetic flux density and reducing themagnetic losses.

In some embodiments, a radial flux electric machine of the currentdisclosure may be an electric motor or an electric generator. Theelectric machine may include a rotor 200 configured to rotate about anaxis of rotation 1000, a plurality of electromagnetic coils 200, and astator 100 (see, e.g., FIGS. 8A-22 ). In some embodiments, the stator100 may have an annular stator ring 130 and a plurality of coretooth-portions 122 extending from the stator ring 130 in a radialdirection (see, e.g., 23A-23K). The annular stator ring 130 and theplurality of core tooth-portions 122 may be integrally formed of a SoftMagnetic Composite (SMC). In some embodiments, the SMC may include oneor more isotropic ferromagnetic materials and have magnetic saturationinduction ≥about 1.6 Tesla and an electrical resistivity ≥about 10 μΩ/m.The stator 100 may include a plurality of multi-part teeth 120symmetrically arranged on the annular stator ring 130, and each tooth120 may include one of the plurality of core tooth-portions 122 and atleast one additional tooth-portion 124A, 124B, 124E, 124F that arenon-integrally formed with the core tooth portion 122 (see, e.g., 23A,23B, 23I-23K). One pair of additional tooth portions 124A, 124B may bepositioned on opposite side surfaces of the core tooth-portion 122 toform a tooth 120 (see, e.g., FIGS. 23A-23C). One pair of additionaltooth portions 124A, 124B may be positioned on opposite side surfaces ofthe core tooth-portion 122 and another pair of additional tooth-portions124E, 124F may be positioned on oppositely positioned top and bottomsurfaces of the core tooth-portion 122 (see, e.g., FIGS. 23I-23K). Insome embodiments, only a single wedge shaped portion may be used as theadditional-tooth portion.

In some embodiments, a cross-section of the core tooth-portion 122 ofeach tooth 120 along a plane perpendicular to the axis of rotation 1000of the electric machine may have a substantially rectangular shape andthe cross-section of each additional tooth portion may have asubstantially triangular shape (see, e.g., FIGS. 23, 23H, 23I). In someembodiments, a cross-section of each of the core tooth-portions 122 andat least one pair of additional tooth-portions 124A-124F along a planeperpendicular to the radial direction may have a substantiallyrectangular shape. A cross-section of each multi-part tooth 120 in aradial plane, or in a plane perpendicular to the axis of rotation 1000,may have a trapezoidal shape. The cross-sectional area of each tooth 120in a plane perpendicular to the radial direction of the tooth 120 mayvary in the radial direction while the perimeter of the cross-sectionalarea remains substantially a constant in the radial direction (see,e.g., FIGS. 26A-26D). In embodiments where the rotor 200 is disposedradially outwards of the stator 100 to form an air gap 250 between therotor 200 and the stator 100 (see, e.g., FIGS. 2, 3 ), thecross-sectional area may increase in the radial direction toward the airgap 250. The cross-sectional area of a tooth 120 in a planeperpendicular to the axis of rotation 1000 may decrease in the axialdirection from the center of the tooth 120 towards its sides (see, e.g.,FIGS. 27A-27D).

In some embodiments, each multi-part tooth 120 defines external surfaceshaving two sets of opposing faces (e.g., faces A, B and faces C, D ofFIG. 23B). The opposing faces of each set of the two sets may benon-parallel to each other. That is, faces A and B may be non-parallelto each other and faces C, D may be non-parallel to each other. In someembodiments, each face of the two sets of opposing faces may be inclinedin a radial direction. The opposing faces of one set of opposing facesmay converge towards each other in a radially outward direction (e.g.,faces A, B of FIG. 23D) and the opposing faces of the other set ofopposing faces diverge from each other in the radially outward direction(e.g., faces C, D of FIG. 23C). Adjacent side faces of adjacent teethmay be parallel to each other. That is, side face C of one tooth 120 maybe parallel to side face D of the adjacent tooth 120 (see, e.g., FIGS.23A-23C).

In some embodiments, the annular stator ring 130 of the electric machinemay include two mirror-symmetric bodies 130A, 130B coupled togetheralong a plane of symmetry perpendicular to the axis of rotation 1000(see, e.g., FIGS. 32B, 32C). The annular stator ring 130 may includemultiple substantially annular components attached together. The twomirror-symmetric bodies 130A, 130B may be attached together along theplane of symmetry using an adhesive material. In some embodiments, thedifference between the coefficients of thermal expansion of materials ofthe two mirror-symmetric bodies (or the SMC) and the adhesive materialmay be less than about 20%.

Any now-known or later-developed SMC may be used to fashion theintegrally formed annular stator ring 130 and the plurality of coretooth-portions 122. In some embodiments, a commercially available SMC(e.g., Sintex® SMC, Somaloy 130i, Somaloy 500, Somaloy 700 IP, Somaloy700 3P, Somaloy 700 5P, or another suitable SMC) may be used. Themagnetic saturation induction of the SMC may be ≥about 2.4 Tesla or≥about 2.5 Tesla. In some embodiments, the resistivity of the SMC may be≥about 100 μΩ/m or ≥about 150 μΩ/m.

Various embodiments of the electric machines of the current disclosuremay include an inner stator and an outer rotor configured to rotateabout the inner stator. As explained previously, electric machines ofthe current disclosure may have different configurations (see, e.g.,FIGS. 8A-22 ). In some embodiments, the electric machine may include aninner stator 100 and an outer rotor 200 (see, e.g., FIGS. 2, 3 ) thatrotates with respect to the stator 100 around the axis of rotation 1000.The electric machines of the current disclosure may include a rotorbase. The rotor base may be part of the rotor. The rotor base refers toany component of the rotor that allows for the coupling of the permanentmagnets of the rotor to the shaft (e.g., shaft 20) of the electricmachine. The electric machine may also include a plurality of annularlyarranged permanent magnets axially extending from the rotor baseparallel to an axis of rotation of the rotor. A permanent magnet may bea magnet that retains its magnetic properties in the absence of aninducing magnetic field or current. Permanent magnet may be object madefrom a material that is magnetized and creates its own persistentmagnetic field. The material from which permanent magnets are made iscalled magnetically hard. It differs from a soft magnetic material by anincreased hysteresis loop. In general, any type of a permanent magnetknown in the art (now known or later developed) may be used to form thepermanent magnets. In some embodiments, the permanent magnets may bemade of a rare earth (RE) material, such as, for example,neodymium-iron-boron (NdFeB), samarium-cobalt (SmCo), etc. Given thehigh cost and relative scarcity of RE materials, in some embodiments,the permanent magnets may be non-RE magnets (e.g., ferrite magnets). Itis also contemplated that, in some embodiments, the permanent magnetsmay be hybrid magnets, where a combination of RE magnets and ferritemagnets are used.

In some embodiments, the electric machine may also include a cylindricalcore extending from the rotor base. In some embodiments, the core may beconfigured to conduct magnetic fluxes. The core may also providestructure for fixing the permanent magnets of the rotor. In someembodiments, the core may extend from the rotor base such that itencircles the plurality of permanent magnets. Although not arequirement, in some embodiments, the core may be formed of a SMC. A SMCcylindrical core may exhibit one or more of three-dimensional (3D)isotropic ferromagnetic behavior. It may also exhibit very low eddycurrent losses and relatively low total core loss at medium and highfrequencies. Additionally, a SMC core may also exhibit improved thermalcharacteristics and a reduced weight. Thus, there may be distinctadvantages for using a SMC core in some disclosed electric machines.

The electric machine may also include a sleeve that encircles the rotor.The sleeve may be a structure that protects the rotor and/or increasesthe strength of the rotor. In some embodiments, the sleeve may be abandage. The sleeve may be in the form of a ring, belt, or anotherannular structure that extends around some or all rotor components. Insome embodiments, the sleeve may protect the rotor components againstthe influence of centrifugal (or centripetal) forces when the rotorrotates. In some embodiments, the sleeve may support the cylindricalcore and the cylindrical core may support the plurality of permanentmagnets. For example, the sleeve may provide structural support for thecore and the core may provide structural support for the plurality ofpermanent magnets. In some embodiments, the cylindrical core may bepositioned radially between the sleeve and the plurality of magnets.

FIG. 34A is an illustration of an exemplary rotor 200 coupled to theshaft 20 of the electric machine 10 (see also FIGS. 2-3 ). As explainedpreviously with reference to FIGS. 1-3 , during operation of theelectric machine 10, the rotor 200 is positioned radially outwards ofthe stator 100, and it rotates with respect to the stator 100 about theaxis of rotation 1000. The rotor 200 may include a rotor base 904. Asillustrated in FIG. 34A, in some embodiments, rotor base 904 may have adisk-like structure. However, a disk-like structure is not arequirement, and the rotor base 904 may have any suitable shape andconfiguration. The rotor base 904 may be fastened (or coupled) to theshaft 20 such that they rotate as one. That is, when the electricmachine 10 operates, both the rotor base 904 and the shaft 20 rotates.

As explained previously (e.g., with reference to FIGS. 1-3 ), one ormore permanent magnets may be suspended from the rotor base 904 (e.g.,see permanent magnets 220 of FIG. 2 ). FIG. 34B is a cross-sectionalview and FIGS. 36 and 37 sectional views of the rotor 200 of FIG. 34A.As can be seen in these figures, the permanent magnets 220 may bearranged to form an annular ring around the axis of rotation 1000. Rotor200 may also include a rotor core 910 and a sleeve 908 that both extendaround the axis of rotation 1000. The core 910 may extend around thepermanent magnets 220, and the sleeve 908 may extend around the core910. Thus, the plurality of permanent magnets 220, the core 910, and thesleeve 908 may form three concentric annular rings around the axis ofrotation 1000. The core 910 may be a cylindrical component with thepermanent magnets 200 mounted on its inner cylindrical wall. The sleeve908 may be a cylindrical component with the core abutting its innercylindrical wall. In some embodiments, the core 910 may be mounted onthe inner cylindrical wall of the sleeve 908. As best seen in FIGS. 34Band 36 , the core 910 may be sandwiched between the plurality ofpermanent magnets 220 and the sleeve 908.

Rotor 200 may also include one or more balancing rings. The term“balancing ring” refers to a structure that assists in the balancing ofthe rotor. In some embodiments, the balancing rings allow for thedynamic balancing of the rotor by redistributing the weight of therotor. For example, in some embodiments, the balancing ring may supportweights (e.g., screws) that can be manipulated (e.g., screwed in or out)to redistribute the weight of the rotor. In some embodiments, abalancing ring 922 may be provided at one end (e.g., top end) of sleeve908 (see FIG. 36 ). Alternatively, or additionally, in some embodiments,a balancing ring 926 may be provided at the bottom end of sleeve 908(see FIG. 37 ). In some embodiments, only one of balancing rings 922,926 may be provided while in other embodiments, both balancing rings922, 926 may be provided. Providing both balancing rings 922, 926 mayenable two-plane balancing or rotor 200. It should be noted that thestructure and location of balancing rings 922, 926 illustrated in thesefigures in only exemplary. In general, one or more balancing rings maybe provided at any location of the rotor 200.

With specific reference to FIG. 34B, in some embodiments, a plurality ofpermanent magnets 220 may be annularly arranged on rotor base 904 suchthat they extend axially from the rotor base 904 parallel to the axis ofrotation 1000 of the rotor 200. The permanent magnets 220 may beradially magnetized and segmented to reduce eddy current losses. Theterm “magnetic axis” indicates an axis of permanent magnet magnetizationof the permanent magnets. The domains are oriented with respect to thisaxis when the magnets are magnetized. As a result, two opposite poles(e.g., north and south poles) of a permanent magnet 220 are formed alongthis magnetic axis. In a permanent magnet, the magnetic axis extendsbetween its north and south poles. In some embodiments, when thepermanent magnets 220 are arranged in a cylindrical pattern as shown inFIGS. 36 and 37 (and FIG. 3 ), the magnetic axis of the individualpermanent magnet 220 may extend in a radial direction. In someembodiments, the magnetic axes of the plurality of permanent magnets 220may intersect each other at (or near) the axis of rotation 1000.

FIGS. 38A and 38B illustrates the core 910 and the permanent magnets 220of the rotor 200. In some embodiments, permanent magnets 220 with radialmagnetization and alternating polarity are fixed or mounted on the innersurface of the cylindrical core 910, for example, using an adhesive(e.g., see also FIG. 3 ). The permanent magnets 220 may be positionedsuch that the north pole of one permanent magnet 220 faces radiallyinwards (i.e., towards the axis of rotation 1000) while the south poleof its adjacent magnets 220 faces radially inwards. In some embodiments,as explained previously (with reference to FIGS. 2-3 ), each permanentmagnet 220 may be made of multiple permanent magnet segments 222attached together. That is, the permanent magnets 220 may be segmentedabout the axis of rotation 1000. In some embodiments, as best seen inFIGS. 38A and 38B, the permanent magnets 220 may also be segmented alongthe axis of rotation (i.e., lengthwise along the axis of rotation 1000).The plurality of the permanent magnets 220 may be annularly arrangedabout the axis of rotation 1000 such that adjacent permanent magnets 220are spaced apart from each other by a spacer 224 (or a gap). FIG. 38Cillustrates an exemplary spacer 224. The spacer 224 may be a solid or ahollow component that separates the adjacent permanent magnet segments220. In some embodiments, the spacer 224 may be made of a non-conductivematerial. Although not a requirement, in some embodiments, the spacer224 may extend the entire length of the core 910. Segmenting thepermanent magnets 220 may assist in the reduction of eddy currentlosses. As explained previously, the permanent magnets 220 may be rareearth (RE) magnets (e.g., NdFeB, SmCo, etc.), ferrite magnets, or otherknown types of magnets.

Outer rotor 200 may also include a cylindrical core 910. The cylindricalcore 910 may extend from rotor base 904 to encircle the plurality ofpermanent magnets 220. In some embodiments, cylindrical core 910 may beformed of a SMC. The cylindrical core 910 may support one side (e.g.,radially outer side) of the plurality of permanent magnets 220. In someembodiments, the permanent magnets 220 may be mounted on the cylindricalcore 910 (e.g., on the radially inner side of the cylindrical core 910).The permanent magnets 220 may be attached to the core 910 using, forexample, an adhesive material. For example, an adhesive layer may bondthe radially outer side of the permanent magnets 220 with the radiallyinner side of the core 910.

Sleeve 908 may encircle the cylindrical core 910. In some embodiments,as illustrated in FIGS. 36 and 37 , the sleeve 908 may extend around theradially outer side of the cylindrical core 910. The sleeve 908 mayphysically contact and support the cylindrical core 910. In someembodiments, an adhesive material may attach the radially inner side ofthe sleeve 908 to the radially outer surface of the core 910. The sleeve908 may support the plurality of permanent magnets 220 (via the core910). Since the sleeve 908 supports the radially outer surface of thecore 910, it may protect the core 910 from cracking due to centrifugalforces during rotation of rotor 200. The core 910 may be positionedradially between sleeve 908 and plurality of permanent magnets 220. Insome embodiments, the sleeve 908 may be attached to the rotor base 904using an adhesive material. In some embodiments, the sleeve 908 may beintegrated with, or made integral with, the rotor base 904 (e.g., thesleeve 908 and the rotor base 904 may be formed as a single part of thesame material).

In some embodiments, the sleeve 908 and/or the rotor base 904 may bemade of aluminum or a non-magnetic composite material like carbon fiber,glass fiber, and/or an aramid fiber like Kevlar. A non-magneticcomposite material is a multicomponent material, non-conductive formagnetic flux and made of two or more components with significantlydifferent physical and/or chemical properties. In general, the sleeve908 and the rotor base 904 may be made of a magnetic material or anon-magnetic material. The non-magnetic material (of the sleeve 908and/or the rotor base 904) may be a composite material. In someembodiments, the composite non-magnetic material may include at leastone of carbon fiber, glass fiber, aramid fiber, Kevlar, or anothersuitable fiber. For example, fibers (carbon, glass, aramid, Kevlar,etc.) may be weaved together to form the sleeve 908. In some suchembodiments, the sleeve 908 may be in the form of a bandage. The bandagemay be flexible, semi-flexible, or rigid. In some embodiments, thefibers may be embedded in a matrix of another material (e.g., an epoxy,etc.) to form the composite non-magnetic material. In some embodiments,the non-magnetic material (of the sleeve 908 and/or the rotor base 904)may include (or be) at least one of stainless steel or aluminum. In someembodiments, the sleeve 908 and/or the rotor base 904 may be made of amagnetic material. The magnetic material may include a soft magneticmaterial, such as, for example, laminated electrical steel sheets. Insome embodiments, the magnetic material may be steel. In someembodiments, the sleeve 908 and the rotor base 904 may be a singleintegrated part made of, for example, steel.

In some embodiments, the sleeve 908 may be assembled as a package withthe core 910 and the permanent magnets 220. In some embodiments, sleeve908 may include a stiffening rib disposed on a recess formed on anexternal surface of the cylindrical core 910. The term “stiffening ribs”indicates elements or features configured to increase the strength ofthe rotor structure. In some embodiments, sleeve 908 may extend over thebalancing ring 926 and the free end of the plurality of permanentmagnets 220. In some embodiments, the sleeve 908 may extend over thebalancing ring 922. In some embodiments, the cylindrical core 910 mayextend from a first end coupled to rotor base 904 to a second end. See,for example, FIGS. 34A-34B. In some embodiments, the balancing rings922, 926 may extend around a free end of the cylindrical core 910.

FIG. 35 illustrates an exemplary shaft 20 that is configured to rotateabout the axis of rotation 1000 of FIGS. 2, 3 ). FIGS. 36-37 illustratepartial views of exemplary outer rotor 200. Outer rotor 200 includesfirst balancing ring 922 and second balancing ring 926. The firstbalancing ring 922 may be disposed at a first end of cylindrical core910 coupled to rotor base 904. The second balancing ring 926 may bedisposed at a second end of cylindrical core 910 opposite rotor base904. In some embodiments, the second balancing ring 926 may providedynamic balancing of the rotor 200, and the first balancing ring 922 mayprovide a static balancing. First and second balancing rings 922, 926may be configured to be attached to sleeve 908 and/or the cylindricalcore 910. One or both of the balancing rings 922, 926 may include holes924.

Cylindrical core 910 together with the permanent magnets 220 may beattached to rotor base 904, which couples rotor 200 to shaft 20. In someembodiments, the sleeve 908 may be folded around the end of cylindricalcore 910 and permanent magnets 220, clamping them on both end sides ofouter rotor 200 (see, e.g., FIG. 36 ). In some embodiments, the sleeve908 may be made of a non-conductive material, or a material with a lowelectrical conductivity, or a non-magnetic non-conductive compositematerial. In some embodiments, cavities or holes may be drilled in theseweights during precise static and dynamic balancing. In someembodiments, the required weight changes may be made in two planes(e.g., using the two balancing rings 922 and 926). Weights may beinstalled into balancing ring holes 924. In some embodiments, secondbalancing ring 926 may be located at the first end of cylindrical core910 (the end that is coupled to rotor base 904). In some embodiments,the first and/or second balancing rings 922, 926 may be formed of anon-magnetic composite material. In some embodiments, the first and/orsecond balancing rings 922, 926 may be formed of a non-magneticmaterial. In some embodiments, the first and/or second balancing rings922, 926 may include one or more screws for balancing the outer rotor200.

In some embodiments, plurality of permanent magnets 220 may be arrangedon rotor base 904 in a substantially circular pattern around the axis ofrotation 1000 (see, e.g., FIGS. 3, 36-38B). Adjacent magnets 220 areseparated by a spacer 224, made of non-magnetic material or any softmagnetic material like a SMC. In some embodiments, plurality ofpermanent magnets 220 are arranged on rotor base 904 such that amagnetic axis of each permanent magnet of plurality of permanent magnets220 extend towards the axis of rotation (e.g., axis of rotation 1000).In some embodiments, the plurality of permanent magnets 220 are arrangedon rotor base 904 such that a magnetic axis of each permanent magnet ofplurality of permanent magnets 220 intersect at (or proximate to) theaxis of rotation.

In some embodiments, rotor base 904 may be formed of aluminum or steel.In some embodiments, the rotor base 904 may be integral with sleeve 908and one or more balancing ring (e.g., 922, 926). The plurality ofpermanent magnets 220 may be attached to cylindrical core 910 using anadhesive. In some embodiments, a difference between coefficients ofthermal expansion (CTE) of materials of plurality of permanent magnets220, cylindrical core 910, and the adhesive may be less than about 20%to reduce CTE mismatch induced thermo-mechanical stresses during thermalexcursions. The cylindrical core 910 may be attached to rotor base 904using an adhesive. The electric machine may be an electric motor or anelectric generator. In some embodiments, cylindrical sleeve 910 may bemade in the form of a package assembled from laminated sheets ofelectrical steel.

FIG. 38D illustrates a view of exemplary cylindrical rotor core 910. Asexplained previously, in rotor 200, spacers 224 separate adjacentpermanent magnets 220 in the plurality of permanent magnets 200 mountedon the inside surface of the cylindrical core 910 (see FIG. 38A-38C). Asan alternative to (or in addition to) spacers 224, in some embodiments,the cylindrical core 910 may include integrated spacers 928. Thesespacers 928 may protrude inward in a radial direction from the insidecylindrical surface of the core 910. The integrated spacers 928 maydefine slots 929 therebetween to house the permanent magnets 220therein. When the permanent magnets 220 are mounted on these slots 929,the spacers 928 separate adjacent permanent magnets 220 in the pluralityof permanent magnets 200 mounted on the inside surface of thecylindrical core 910. FIGS. 42A-42B illustrate cross-sectional views ofexemplary outer rotor 200 in the radial plane. As illustrated in thesefigures, when the permanent magnets 220 are disposed in the slots 929(see FIG. 38D) between the spacers 928 on the inside surface of therotor core 910, the spacers 928 separate adjacent permanent magnets 220from each other in the circumferential direction. The spacers 928 mayhave any thickness in the radial direction. In some embodiments, thethickness of the spacers 928 may not exceed the thickness of thepermanent magnets 220 (in the radial direction) so that the spaces 928do not protrude into the air gap 250 between the outer rotor 200 and theinner stator 100 (see FIG. 3 ). In some embodiments, to limit thepulsating moment, the thickness of each spacer 928 may be such that itis less than or equal to about half the thickness of a permanent magnet220.

FIG. 39 illustrates a cross section view of the rotor 200. Sleeve 908may be installed in rotor 200 by any method. In some embodiments, toinstall the sleeve 908, stops 930 may be provided on the two ends (e.g.,top and bottom ends) of the rotor 200 (e.g., on either side of sleeve908). In embodiments where sleeve 908 is in the form of a bandage, thesleeve 908 may be installed on the rotor 200 by winding (or wrapping)the sleeve material around the outer surface of rotor core 910 (see FIG.40 ). The winding may be performed such that each protrusion and eachdepression on a surface of core 910 (or the outer surface of the rotor)are filled in one operation. This winding may serve to increase thestrength and rigidity of rotor 200 during operation and to reducevibration and noise. The winding (as shown in FIG. 40 ) may be done witha composite tape, with a composite thread (not shown), or a combinationof both. Although the use of stops 930 to form the sleeve 908 isdescribed, this is only exemplary. The winding may also be accomplishedwithout the stops 930.

In some embodiments, the rotor base 904 the sleeve 908 may be anintegrated component. In such cases, the rotor base 904 and the sleeve908 may be formed together as one integrated part, for example, of acomposite material. In some embodiments, an adhesive material may beused to secure the permanent magnets 220 and/or the spacers 224 oncylindrical core 910, the rotor base 904, the sleeve 908, and thebalancing rings 922, 926. The adhesive material may be selected suchthat its coefficient of thermal expansion (CTE) is close (e.g., about20%) to the CTEs of the materials to be bonded in order to reduce stressduring heating of the bonded elements.

As best seen in FIG. 40 , rotor base 904 may include one or moreventilation holes 932. Ventilation holes 932 may be configured to directair flow along the axis of rotation 1000 (i.e., parallel to the axis ofrotation 1000). In some embodiments, this air is directed into the rotor(towards the stator positioned within the rotor) when the rotor 200rotates (see, e.g., FIG. 2 ). In some embodiments, the ventilation holes932 may be configured to operate as fan blades when rotor 200 rotates tocool one or more components of an electric machine. In some embodiments,blades, vanes, or other air-moving features may be provided around (orproximate) the ventilation holes 932 to direct air along the axis ofrotation 1000 (or into holes 932 and towards the stator during rotorrotation).

FIG. 41 illustrates a view of exemplary outer rotor 200. In someembodiments, to increase the permissible maximum rotational speed of therotor 200, one or more slots 934 may be provided on the outer surface(e.g., radially outer surface) of the cylindrical core 910. As can beunderstood from FIG. 41 , each slot 934 may be positioned opposite themiddle of each of permanent magnet 220 (one permanent magnet 220 isshown using dashed lines in FIG. 41 ). In some embodiments, the innermating surface of the sleeve 908 includes corresponding ribs 936 thatare received in the slots 934 when the core 910 is mounted within thesleeve 908. In embodiments where the sleeve 908 is a bandage that iswrapped around the core 910 (as described with reference to FIG. 40 ),the slots 934 may be configured to receive the material of sleeve 908and form stiffening ribs 936. That is, the portion of the sleeve 908that is received in the slots 934 when the sleeve 908 is mounted orwrapped around the core 910 forms stiffening ribs 936. The stiffeningribs 936 increase the strength of the rotor core 910 without increasingits size (e.g., thickness). The middle of each permanent magnet 220corresponds to the location of the lowest magnetic flux density.Therefore, positioning the slots 934 opposite the middle of thepermanent magnets 220 assists in reducing leakage flux and increasingthe strength of the core 910 without increasing its size. In someembodiments, the rotor 200 may be made without a sleeve 908.

FIG. 43 illustrates a view of exemplary outer rotor 200 having a rotorbase 904, a cylindrical core 910, a plurality of permanent magnets 220,and a sleeve 908. As illustrated in FIG. 43 , the cylindrical core 910may have a non-uniform thickness (in the radial plane) about the axis ofrotation 1000. In the illustrated embodiment, the outer surface of thecylindrical core 910 forms an undulating surface (with its radiusvarying, or increasing and decreasing, about the axis of rotation 1000)and the outer surface of the core 910 is a cylindrical surface. Thenon-uniform thickness of the core 910 occurs as a result of thedifferent types of inner and outer surfaces. In the illustratedembodiment, the outer surface of the sleeve 908 is cylindrical and itsinner surface (that mates with undulating outer surface of the core 910)is a corresponding undulating surface. Thus, the sleeve 908 also has anon-uniform thickness (i.e., a varying thickness about the axis ofrotation 1000) as a result of the difference between its inner and outersurfaces.

As can be seen in FIG. 43 , a thicker region X (or a location of higherthickness) of cylindrical core 910 corresponds to the thinner region (orthe location of lower thickness) of the sleeve 908, and thinner region Yof the core 910 corresponds to a thicker region of the sleeve 908. Ascan be seen in FIG. 43 , the thicker region X of core 910 is positionedbetween adjacent permanent magnets 220 and the thinner region Y of thecore 910 is positioned adjacent to the middle of each permanent magnet220. Also, the thicker region of the sleeve 908 is positioned adjacentto the middle of each permanent magnet 220 and its thinner region ispositioned between two permanent magnets 220. The middle of a permanentmagnet 220 corresponds to the location of the lowest magnetic fluxdensity. Positioning the thicker regions of the sleeve 908 adjacent to(or proximate) the middle of each permanent magnet 220 increases thestrength of the rotor 200 without increasing its size. It should benoted that the undulating outer surface of the core 910 and the innersurface of the sleeve 908 in exemplary embodiment of rotor 200 discussedwith reference to FIG. 43 is only exemplary. In general, a non-uniformthickness of the core 910 and/or sleeve 908 may be provided in anymanner. In some embodiments, the thickness of the core 910 and/or sleeve908 may vary, for example, in a step-wise manner in the circumferentialdirection (i.e., about the axis of rotation 1000).

FIG. 44 illustrates an exemplary core 910 of a rotor 200. In theillustrated embodiment, permanent magnets 220 are disposed (or embedded)in the core 910. In some embodiments, the permanent magnets 220 may bedisposed in a star pattern in the core 910. The core 910 may includeslots in a corresponding star pattern to receive the permanent magnets220. It should be noted that the star pattern is only exemplary, and ingeneral, the permanent magnets 220 may be disposed in any pattern (e.g.,circular, etc.) in the core 910. In some embodiments, the core 910 mayinclude circumferentially spaced-apart slots to receive permanent magnetsegments.

With reference to FIGS. 4A-4C and FIGS. 6A-7C, for efficient operationof the electric machine, it is preferable that the inner surface of theelectromagnetic coil 300 that is mounted on a multi-part tooth 120contacts, or is snug against, the outer surface (surface A, B, C, D ofFIG. 23B) of the tooth 120. Because of the trapezoidal shape (or thevarying cross-sectional area of the tooth 120 in the radial direction)of the tooth 120, it is difficult to mount a pre-fabricated coil 300 onthe tooth 120 such that the mating surfaces of the cavity 320 of thecoil 300 (see, e.g., FIGS. 6A-7C) and the external surface of the tooth120 contact along the entire radial direction of the tooth. While it maybe possible to wind a wire (or a foil) directly onto the tooth 120 (oron a pre-assembled core 110 with teeth 112) to form a coil 300, such aprocess would increase manufacturing cost. Winding a wire on the tooth120 would also decrease the filling density of the slot 160 between theteeth 120 (see, e.g., FIGS. 4A-4B) and result in a low fill factor ofthe electric machine. Forming the tooth 120 of multiple parts (asdiscussed above) enables a prefabricated coil 300 to be installed, ormounted, on the tooth 120 while maintaining a high fill factor value.The parts of the multi-part tooth 120 are assembled inside the coil 300to form the trapezoidal shape of the tooth 120 inside the cavity 320 (orthe opening) of the coil 300.

FIGS. 45A-45F illustrate an exemplary method of mounting (or installing)a coil 300 on an exemplary multi-part tooth 120. FIGS. 46A-46C aresimplified schematic illustrations depicting different stages duringmounting a coil 300 on tooth 120. In the discussion below, referencewill also be made to FIGS. 46A-46C. In the discussion below, the methodof installing the coil 300 on the embodiment of tooth 120 described withreference to FIG. 24A will be described. Coils 300 can also be installedin other embodiments of teeth 120 in a similar manner. In theillustrated embodiment, the multi-part tooth 120 that includes adiscrete core tooth-portion 122 (i.e., a core tooth-portion 122 which isnot integrated with the annular part 130 of core 110 as in theembodiment of FIG. 23A) with a groove 138 on its base 134, and twoadditional tooth-portions 124A and 124B. A pre-fabricated (pre-formed,pre-wound, etc.) coil 300 may be installed on the multi-part tooth 120formed of these multiple tooth portions 122, 124A, 124B. Although not arequirement, in the illustrated embodiment, the two additionaltooth-portions 124A, 124B are identical.

The tooth 120 is made of multiple parts such that the previously formedcoil 300 can be mounted on the tooth 120 such that the multiple parts ofthe tooth 120 fits within the cavity 320 of the coil 300. With referenceto FIG. 45A, the pre-formed coil 300 includes an electrical conductor(wire, foil, etc.) that extends around a central cavity 320 (or opening)of the coil 300. The cavity 320 extends from a first end 322 to a secondend 324 of the coil 300. In some embodiments, each additionaltooth-portion 124A, 124B may be identical in structure and may bewedge-shaped. Each additional tooth-portion 124A, 124B may extend from abroader end 128 to a narrower end 126. After assembly, the first end 322of coil 300 will be positioned proximate the stator core 110 and itssecond end 324 will be positioned proximate the air gap 250 (see FIG. 2).

In some embodiments, the method for installing the coil 300 on themulti-part tooth 120 incudes inserting at least one additionaltooth-portion 124A, 124B of the multi-part tooth 120 into the cavity 320of the coil 300 such that a broader second end 128 of the insertedadditional tooth-portion(s) 124A, 124B extends out of the cavity 320.For example, as best seen in FIG. 46A, the two additional tooth-portions124A, 124B are inserted into the cavity 320 of the coil 300 such thatthe broader second ends 128 of the two additional tooth-portions 124A,124B extents (or protrudes) from the cavity 320 through its second end324. In embodiments where the tooth 120 includes only a singleadditional tooth-portion (e.g., tooth portions 124C, 124D of FIGS. 23Eand 23H), this single tooth portion will be inserted into the cavity 320of the coil 300 such that its broader end protrudes out from one end ofthe cavity 320. In embodiments where the tooth 120 includes multipleadditional tooth-portions (see FIGS. 23A, 23I-23K), one or more of thesemultiple additional tooth-portions will be inserted into the cavity 320.

In some embodiments, as illustrated in FIG. 45A-46C, both the additionaltooth-portions 124A, 124B are inserted into the cavity 320. The twoadditional tooth-portions 124A, 124B may be pressed against the oppositeside walls of the cavity 320 (i.e., against the inner walls of the coil300) such that a gap is formed in the cavity 320 between the twoadditional tooth-portions 124A, 124B. That is, as can be seen in FIGS.45D and 46A, the two additional tooth-portions 124A and 124B are placedin the cavity 320 such that a side surface of each additionaltooth-portion 124A, 124B contacts (or is pressed against) an oppositesurface on the inside of the cavity 320 to form a gap between the twoadditional tooth-portions 124A, 124B.

As best seen in FIGS. 45D and 46A, the additional tooth-portions 124A,124B are inserted into the cavity 320 such that the broader second end128 of the inserted tooth portion 124A, 124B extends out (or protrudesfrom) of the cavity 320 at its second end 324. As best seen in FIG. 46B,the coil 300 (with the inserted additional tooth-portions 124A, 124B isthen mounted on the core tooth-portion 122 of the multi-part tooth 120such that the broader second end 128 of the inserted additionaltooth-portion 124A, 124B remains extended out of the cavity 320 of thecoil 300. As illustrated in FIG. 46C, a force F is applied on theprotruding second ends 128 of the additional tooth-portion 124A, 124B topush the additional tooth-portions further into the cavity 320 (i.e.,towards the first end 322 of the cavity 320). As the additionaltooth-portion 124A, 124B enters further into the cavity 320, they pressagainst the sides of the core tooth-portion 122 and the inner walls ofthe cavity 320 to tighten the coil on the multi-part tooth 120 (see,e.g., FIG. 45E, 46C). In some embodiments, as illustrated in FIG. 45F,an adhesive material (or a glue) may then be applied to couple themultiple parts of the multi-part tooth 120 together and to the innerwalls of the coil cavity 320.

It should be noted that the embodiment discussed above is onlyexemplary. There may be many variations to the described method based onthe configuration of coil and the tooth. FIGS. 23E-23F and FIG. 23H alsodepict an exemplary method of installing a coil 300 on some otherconfigurations of multi-part tooth 120. As explained previously,additional tooth-portion 124C (of FIG. 23E) or 124D (of FIG. 23H) mayfirst be inserted into cavity 320 of coil 300 such that the broader endof the additional tooth-portion 124C or 124D extends out of opening 320.The coil 300 with the additional tooth-portion 124C or 124D may then bepositioned over the core tooth-portion 122 such that broader end of theadditional tooth-portion 124C or 124D remains extended out of the cavity320. A force may then be applied to the broader end of the additionaltooth-portion 124C or 124D to push it further into the cavity 320thereby snugly fitting the coil 300 around the multi-part tooth 120.Application of the force may drive the broader end of the additionaltooth-portion 124C or 124D further into coil 300 towards the annularpart 130 of core 110 to tighten the coil 300 on the multi-part tooth 120(see, e.g., FIG. 23F). In some embodiments, adhesive material may thenbe applied to couple the multiple parts of the multi-part tooth 120together.

FIGS. 23I-23J illustrate another exemplary method of installing a coil300 on a multi-part tooth 120. As in the embodiment described withreference to FIG. 45A-46C, a pair of additional tooth-portions 124A and124B may first be positioned in the cavity 320 of coil 300 (see FIG.23J). In this configuration, the broader end of the two additionaltooth-portions 124A and 124B may protrude or extend out of the cavity320 (see, FIG. 23J). The core tooth-portion 122 with the additionaltooth-portions 124E, 124F positioned on its opposite sides (e.g., topand bottom sides, see FIG. 23J) may then be inserted into the cavity 320of the coil 300 through the space between the two additionaltooth-portions 124A, 124B. When the core tooth-portion 122 is insertedinto the cavity 320, the broader ends of one or both of the additionaltooth-portions 124A, 124B may remain protruded out of the cavity 320. Aforce may then be applied to push at least a portion of the protrudingbroader end(s) into the cavity 320. As the additional tooth-portion(s)124A, 124B enters further into the cavity 320, they press against thesides of the core tooth-portion 122, the additional tooth-portions 124E,124F, and the inner walls of the cavity 320 to tighten the coil 300 onthe multi-part tooth 120 (see, e.g., FIG. 23K). In some embodiments, anadhesive material may then be applied to couple the parts together withthe coil. Any type of adhesive material may be used to couple the partsof the multi-part tooth 120 together. In some embodiments, the adhesivematerial may have a coefficient of thermal expansion close to thecoefficient of thermal expansions of the tooth and/or the coil materialsto reduce the CTE mismatch induced thermo-mechanical stresses when theparts heat up during operation. In some embodiments, the CTE mismatchbetween the adhesive material and the different parts of the multi-parttooth 120 may be below about 20%.

The described methods of mounting the coil 300 on a multi-part tooth 120is applicable to embodiments of tooth 120 where the core tooth-portion122 is separate from the core 110 (e.g., the embodiments of FIGS. 23Land 23M) and to embodiments of tooth 120 where the core tooth-portion122 is integrated with the core 110 (e.g., the embodiments of FIGS.23A-23K). In general, the method of assembling a coil on anirregular-shaped multi-part tooth of an electric machine may includeinserting at least one additional tooth portion (e.g., a wedge-shapedtooth portion or a wedge-portion) of the multi-part tooth into anopening of the coil such that a broader end of the at least onewedge-portion extends out of the cavity (or opening) in the coil. Asused herein, the term “irregular-shaped” refers that the cross-sectionthat varies along the length. In some embodiments, irregular-shapedvolume may best be described by a geometric figure other than regular orsimple figures (circle, cylinder, cube, parallelepiped, etc.). The term“wedge-portion” indicates a part having a broader end and a narrowerend. In some embodiments, the wedge-portion may be in the form of awedge. The term “cavity” or “opening” refers to an inner hollow part ofthe coil. The coil with the inserted at least one wedge-portion ispositioned on a core tooth portion of the multi-part tooth such that thebroader end of the at least one wedge-portion remains extended out ofthe cavity in the coil. The method may also include exerting a force onthe broader end of the at least one wedge-portion to tighten the coil onthe multi-part tooth.

In some embodiments, exerting a force on the broader end of the at leastone wedge-portion may include pushing the broader end of the at leastone wedge-portion into the cavity of the coil (i.e., the coil opening).In some embodiments, the opening in the coil may extend from a first endto a second end. And inserting the at least one wedge-portion mayinclude inserting the at least one wedge-portion into the opening suchthat the broader end extends out of the second end of the opening. Insome embodiments, exerting the force may include pushing the broader endtowards the first end of the opening. The opening or the cavity in thecoil may extend from a first end to a second end. In some embodiments, awidth of the opening at the first end may differ from the width of theopening at the second end, and a length of the opening at the first endmay differ from a height of the opening at the second end. In someembodiments, a shape of the opening at the first end and the shape ofthe opening at the second end may be rectangular (see, e.g., FIG. 7B).Since the electromagnetic coil fits snugly on the surface of a tooth, insome embodiments, the shape of the coil cavity or opening may correspondto (or may be substantially similar to) the shape of the tooth.Therefore, a perimeter of the opening at the first end of the coilcavity may be substantially the same as the perimeter of the opening atthe second end of the coil cavity (see, e.g., discussion of the shape oftooth 120 with reference to FIGS. 26A-26B). In some embodiments, an areaof the coil opening at the first end may vary from the area of theopening at the second end. In some embodiments, the area of the coilopening may increase from the first end to the second end. In someembodiments, inserting at least one wedge-portion into the coil openingmay include inserting at least two wedge-portions into the opening.

Mounting the coil on a tooth may include mounting the coil on the coretooth portion such that the core tooth portion is disposed between theat least two wedge-portions. In some embodiments, an adhesive materialmay be used to attach the at least two wedge portions and the coretooth-portion of the multi-part tooth together. The multi-part tooth maybe a part of a stator of the electric machine. In some embodiments, thecore tooth portion of the multi-part tooth may be one of a plurality ofcore tooth portions symmetrically arranged on an annular stator ringthat extends around a central axis of the electric machine. The coretooth portion may extend outward in a radial direction from the annularstator ring. In some embodiments, the plurality of core tooth-portionsare integrally formed with the annular stator ring. In some embodiments,in a plane perpendicular to the central axis, the core tooth portion mayhave a substantially rectangular cross-sectional shape and the at leastone wedge-portion may have a substantially triangular cross-sectionalshape (see, e.g., FIG. 23B, 23F, 23K). In some embodiments, in a planeperpendicular to the radial direction, the core tooth portion and the atleast one wedge-portion may have a substantially rectangularcross-sectional shape. In some embodiments, the coil may include awinding of a copper wire around the coil opening or cavity (see, e.g.,7A-7C). The wire may have one of a square, rectangular, or circularcross-sectional shape (see, e.g., 7D, 7E). In some embodiments, the coilmay include a winding of a copper stranded wire in a spiralconfiguration around the opening. In some embodiments, the electricmachine may be an electric motor. In some embodiments, the methodwherein the electric machine may be an electric generator.

An exemplary method of assembling a coil on an irregular-shapedmulti-part tooth of an electric machine may include a step of insertingat least one wedge-portion of the multi-part tooth into an opening ofthe coil such that a broader end of the at least one wedge-portionextends out of the opening in the coil. The method may include a step ofmounting the coil with the inserted at least one wedge-portion on a coretooth portion of the multi-part tooth such that the broader end of theat least one wedge-portion remains extended out of the opening in thecoil. The method may include a step of exerting a force on the broaderend of the at least one wedge-portion to tighten the coil on themulti-part tooth.

FIG. 47 illustrates a flow chart of an exemplary method of installing acoil on a multi-part tooth. With additional reference to FIGS. 45A-46C,the method may include a step of inserting at least one wedge-portion(e.g., additional tooth-portion 124A, 124B) of a multi-part tooth 120into an opening (e.g., cavity 320) of a coil 300 such that a broader end(second end 128) of the at least one wedge-portion extends out of theopening in the coil (step 810). The method may also include a step ofmounting the coil 300 with the inserted at least one wedge-portion 124A,124B on a core tooth portion 122 of multi-part tooth 120 such that thebroader end of the at least one wedge-portion remains extended out ofthe opening in the coil (step 820). The method may further includeexerting a force (e.g., Force F of FIG. 46C) on the at least onewedge-portion 124A, 124B to push its broader end 128 into the opening inthe coil. In method of assembling outer rotor assembly, the opening inthe coil may extend from a first end to a second end, wherein insertingthe at least one wedge-portion includes inserting the at least onewedge-portion into the opening such that the broader end extends out ofthe second end of the opening and the step of exerting the forceincludes pushing the broader end towards the first end of the opening(step 830).

Exemplary methods of forming coils 300 for electric machines of thecurrent disclosure are described below. In some embodiments, the coilsmay be irregular shaped coils. As used herein, the term irregular shapedcoil indicates that the cross-section of the coil varies along itslength. As explained previously with reference to FIGS. 6A-7C, coils 300of the current disclosure may include a cavity 320 that extends from afirst end 322 to a second end 324. In some embodiments, a dimensionrelated to the cross-section of the cavity 320 of an irregular shapedcoil varies along at least a portion of the distance (e.g., length)between the first and second ends 322, 324. In some embodiments, thecross-sectional area varies from the first to the second end 322, 324.Various embodiments of forming irregularly shaped coils of the currentdisclosure may include forming a coil, winding a wire around a mandrelto form the coil in the shape of the mandrel, removing the coil from themandrel, and exerting a mechanical force on the coil to change the shapeof the coil to correspond to the shape of a tooth. The tooth may be partof the stator or the rotor or the electric machine. In some embodiments,the coil may then be mounted on the tooth.

As used herein, the term “mandrel” refers to a device (shaft, spindle,or workpiece) upon which the wire or foil that forms the coil issupported or wound to form a coil of the first shape. In someembodiments, the mandrel may be a shaft or a rod (e.g., a cylindricalshaft). Any type of mechanical force (compressive force, tensile force,pulling, pushing, etc.) may be applied to the coil to change its shape.In some embodiments, the mechanical force may result in deformation ofthe coil. As explained previously with reference to FIGS. 6A-7E, thecoils 300 of the current disclosure may be made of wires or foils. Insome embodiments where the coil is made of a wire, the wire may includea single-strand wire or a multi-strand wire. The term “strand” refers toa current or electrical conductor isolated from other current conductorsof the wire. The term current or “electrical conductor” refers to amaterial or an object that allows for the flow of charge or current inone or more directions. In some embodiments, the wires that form a coilmay be twisted together. That is, the strands of the wires may betwisted together. In some cases, twisting the strands together mayassist in reducing eddy current losses.

FIGS. 48A-48D illustrate the steps of fabricating a coil 300 in anexemplary embodiment. As shown in FIG. 48A, coil 300 may be made from awire 314. Wire 314 may be single-strand wire or a multi-strand wire 314.Coil 300 may be wound in a form of a spiral in the radial direction. Insome embodiments, coil 300 may be wound around a cylindrical mandrel toform spiral shaped winding. As such, a first shape of coil 300 afterwinding on a cylindrical mandrel may correspond to the shape of themandrel. The cylindrical cavity of the coil 300 that results afterwinding on the cylindrical mandrel may have a constant perimeter and aconstant cross-sectional area along the length of the cavity. It shouldbe noted that the cylindrical mandrel and the resulting cylindricalshape are only exemplary. In general, the mandrel may have any shape(i.e., a rod of any cross-sectional shape), and the coil that resultsfrom winding on that mandrel may have a corresponding cross-sectionalshape. For example, if the mandrel used to wind the wire has arectangular cross-sectional shape, the cavity of the coil that resultsfrom that winding operation will also have a substantially similarrectangular cross-sectional shape.

As shown in FIG. 48B, coil 300 may be placed on a fabrication station952 using one or more separation mandrels 956. The separation mandrels956 may support the coil during application of mechanical force tochange the shape of the coil cavity from the first to the second shape.In some embodiments, a mount 954 may affix a portion of coil 300 to thestation 952 so that coil 300 may not move during fabrication. As shownin FIG. 48C, a wedge mandrel 958 may be driven between the separationmandrels 956 to change the shape of coil 300. The wedge mandrel 958 maybe pushed into the cavity of the coil through the gap between the twoseparation mandrels 956 (see FIGS. 48B and 48C) to push diametricallyopposite ends of the internal cavity walls outward. Force may be appliedto wedge mandrel 958, for example, in a downward direction 960 as shownin FIG. 48C to push the wedge mandrel 958 into the space between theseparation mandrels 956. As the wedge mandrel 958 moves downward intothe coil cavity, the separation mandrels 956 may be driven outwards(shown using arrows in FIG. 48C) by the wedge faces of wedge mandrel958. As the separation mandrels 956 moves outward, the internal walls ofthe coil cavity may also be pushed outward. As a result of this force inthe radially outward direction on diametrically opposite ends of thecoil cavity, as shown in FIG. 48D, a second shape of coil 300 may beformed. The second shape may correspond to a shape of a tooth 120. Thatis, after application of the force (as shown in FIGS. 48B-49D), similarto the external shape of a tooth 120 (explained with reference to FIGS.48A-49D), the cavity 320 of the coil 300 that snugly fits on the surfaceof the tooth 120 may have a substantially constant perimeter along itslength from the first end 322 to the second end 324 while itscross-sectional area along the length varies. The second shape may berectangular or trapezoidal. In some embodiments, the cavity 320 may havea trapezoidal 3-dimensional shape with a rectangular cross-sectionalarea in planes perpendicular to an axis that extends between the firstand second ends 322, 324 of the coil 300 (see, e.g., FIGS. 6C, 7A,48B-48D). In some embodiments, at least one end of the internal cavityof coil 300 may expand (or plastically deform) as a result of the forceapplied by wedge mandrel 958. An exemplary embodiment of a coil 300 withits cavity 320 in the second shape is shown in FIGS. 6A-6D and 7A-7B. Asexplained previously, although a wire 314 is used to form the coil 300in the method described above, a coil 300 may also be similarly formedusing a foil 312.

FIGS. 49A-49D illustrate another exemplary method of fabricating a coil.As shown in FIG. 49A, coil 300 may be placed on fabrication station 952using one or more guide separation mandrels 962. Mount 954 may affix aportion of coil 300 so that coil 300 may not move during fabrication. Asshown in FIG. 49B, separation mandrel 962 may include lower portion 964and upper portion 966. Lower portion 964 may be driven inside of a coilto shape the coil and upper portion 966 may be configured to restrictmovement of separation mandrel 962 such as to keep separation mandrel962 against mount 954. As shown in FIG. 49C, wedge mandrel 958 may bedriven between guide separation mandrels 962 to change a shape of coil300. Force may be applied to mandrel 958 opposite fabrication station952 (e.g., in direction 958 downward as shown), and separation mandrels962 may be driven by the wedge faces of wedge mandrel 958. As shown inFIG. 49D, a second shape of coil 300 may be formed. The second shape maycorrespond to a shape of a tooth 120. The second shape may be similar tothat described above. In some embodiments, at least one end of theinternal cavity of coil 300 may expand as a result of the force appliedby wedge mandrel 958. The resulting second shape of coil 300 may besimilar to that shown relative to coil 300 shown in FIGS. 6A-6D and7A-7B.

As explained previously (with reference to FIGS. 45A-46C), a coil 300 ismounted on a tooth 120 of a rotor or a stator such that the cavity 320of the coil 300 fits snugly on the tooth 120. In some embodiments, aftera coil 300 is formed as described above (e.g., with reference to FIG.48A-48D or 49A-49D), the shape of its cavity 320 may not sufficientlycorrespond to the shape of the tooth 120. In some such embodiments,after the coil 300 is formed as described above, a force may be appliedto the external surfaces of the coil 300 and/or the internal walls ofits cavity 320 to finish (or fine-tune) the shape the cavity 320 to theshape of the tooth 120. FIGS. 50A-50D illustrate views of an exemplarymethod of fabricating a coil. As shown in FIGS. 50A-50B, a coil 300(after changing the shape of its cavity to the second shape as describedwith reference to 48A-48D and 49A-49D) may be placed on protrusion 576with its cavity around the protrusion. Forming blocks 572, 574 maycontact and apply a mechanical force (e.g., a compressive force) on theexternal surfaces of the coil 300 to change a shape of coil 300 oncecoil 300 is positioned on protrusion 576. As shown in FIGS. 50C-50D,forming blocks 572, 574 may be driven inwards (e.g., with force 578)towards protrusion 576 to change the shape of the coil cavity to finaldesired shape. The resulting shape of coil 300 may be trapezoidal andcorrespond to the shape of the multi-part tooth 120 (described withreference to 48A-49D). In some embodiments, only one pair of oppositelypositioned blocks 574 (or 572) may apply a compressive force on the coil300 mounted on the protrusion 576. In some embodiments, a first pair ofoppositely positioned blocks 574 may apply a compressive force on thecoil 300 while a second pair of oppositely positioned blocks 572 maymerely rest on the coil surface, for example, to prevent it from bulgingin the direction of blocks 572 as a result of the force application.

In some embodiments, a wedge piece may be used to finish the shape ofthe coil cavity to the final desired shape. FIGS. 51A-51B illustrateview of a method of fabricating a coil. As shown in FIGS. 51A-51B, awedge mandrel 582 and base 584 may be used to finish the shape of thecavity 320 of the coil 300. In some embodiments, the wedge mandrel 582may be moved (e.g., up and down in FIG. 51A) in the cavity 320 of thecoil 300 to finish (or fine-tune) the inner walls of the cavity 320 tothe final desired shape. In some embodiments, as illustrated in FIG.51B, wedge mandrel 582 may be pressed to one side of coil 300 againstbase 584 to finish the shape of one side of the coil cavity to the finaldesired shape. In some embodiments, coil 300 may be flipped and theprocess repeated to form or finish the other side. Mandrel 582 may bewedge shaped so as to form a trapezoidal inside of coil 300. In someembodiments, a mechanical force may be used to decrease the size of theinternal cavity at the other end (e.g., a clamp) while mandrel 582 ispressed against base 584. In such embodiments, mandrel 582 may be actingin a direction away from a central axis of coil 300 (e.g., axis 2000shown in FIG. 6D), and the mechanical force to decrease the size of theinternal cavity at the other end may be acting in a direction towardsthe central axis of coil 300.

FIG. 52 illustrates a method 910 of fabricating a coil for mounting on atooth 120 of a stator or a rotor of an electric machine. Steps of method910 may include a step 920 of winding a wire (or a foil) about a mandrelto form a coil having a first shape corresponding to the shape of themandrel. For example, in some embodiments, a wire 314 (or foil 312) maybe wound around a circular rod or a shaft to form (or deform) acylindrical winding of the wire 314 with a cylindrical cavitytherethrough. Steps of method 910 may include a step 930 of removing thecoil having the first shape from the mandrel. For example, in anembodiment where a wire is wound on a circular shaft to form a circularcoil, the coil may be removed from the shaft. In step 920, the materialof the wire may be plastically deformed such that the coil retains itscircular shape when it is removed from the mandrel in step 930. Steps ofthe method may include step 930 of applying a mechanical force on thecoil to change the shape of the coil from the first shape to a shapethat corresponds to the tooth. For example, if the tooth has arectangular shape, in this step, a mechanical force is applied to thecircular coil of wire so that the shape of its cylindrical cavitychanges to a cavity having a rectangular cross-sectional shape. Steps ofthe method may include step 940 of mounting the coil of the second shapeon the tooth.

In some embodiments, coil the wire may be formed of a number of strandsof an electrical conductor. The wire may have any number (e.g., 2-3000)of strands. In some embodiments, wire 314 may be formed by twistingtogether an electrical conductor or made in the form of a Litz wire. ALitz wire is made of many wire strands which may be individuallyinsulated and twisted or woven together. In some cases, a Litz wire mayassist in distributing a current equally among the multiple wire strandsand thereby reducing its resistance.

Wire 314 may have a circular cross-sectional shape or a rectangularcross-sectional shape. As previously explained, the coils 300 of thecurrent disclosure may be made using a wire 314 or a foil 312. It shouldbe noted that although the above described coil fabricating method 810is described using a wire 314, this is only exemplary. The method 910can also be performed using a foil 312. For the sake of brevity, themethod of fabricating a coil 300 will be described with reference to awire 314. The coil 300 can also be formed using a foil 312 in a similarmanner.

With reference to step 920, the wire 314 may be wound on a mandrel toform a coil having any shape (i.e., any first shape). In someembodiments, the first shape of coil may be a cylindrical shape or atrapezoidal shape. That is, the coil formed as a result of winding thewire 314 on the mandrel may have a cylindrical (or trapezoidal) cavity320 that extends along its length. In some embodiments, the step ofwinding wire 314 about mandrel (i.e., step 920) includes forming a coilhaving an internal cavity 320 extending from a first end 322 to a secondend 324. In some embodiments, the step of applying mechanical force(i.e., step 940) on the coil includes selectively increasing a size ofthe internal cavity 320 at one of the first end 322 or the second end324. In some embodiments, the step of applying the mechanical force(i.e., step 940) on the coil may include changing a shape of theinternal cavity 320. For example, the cross-sectional shape of theinternal cavity 320 may be changed from one shape (e.g., circularcross-sectional shape) to a different shaped (e.g., rectangularcross-sectional shape). In some embodiments, changing the shape of theinternal cavity may include changing a cross-sectional shape of theinternal cavity along a plane perpendicular to a central axis of theinternal cavity from a circular shape (see, e.g., FIG. 49A) to atrapezoidal shape (see, e.g., FIGS. 50C-50D).

In some embodiments, a width and a height of the trapezoidal shape bothmay vary from the first end to the second end (see, e.g., FIGS. 7B,48A-48D). In some embodiments, a perimeter of the trapezoidal shape maybe substantially a constant from the first end to the second end and anarea of the trapezoidal shape varies from the first end to the secondend. In some embodiments, the area of the trapezoidal shape increasesfrom the first end to the second end. In some embodiments, the step ofapplying a mechanical force 930 on the coil may include inserting asecond mandrel into the internal cavity of the coil to change a shape ofthe first end of the internal cavity compared to a shape of the secondend of the internal cavity. The term “second mandrel” indicates a solidmaterial configured to change the shape of the coil from cylindrical totrapezoidal.

The step of applying a mechanical force 930 on the coil may includeapplying a first mechanical force (e.g., mechanical force in direction960) to increase a dimension of the internal cavity at one of the firstend or the second end and a second mechanical force to decrease adimension of the internal cavity at the other of the first end or thesecond end. In some embodiments, the first mechanical force may acttowards a central axis of the internal cavity and the second mechanicalforce acts away from the central axis. In some embodiments, the step ofapplying a mechanical force 930 on the coil includes stretching the wireof the coil that defines at least one of the first end or the second endof the internal cavity. In some embodiments, the wire may be made ofcopper.

Various embodiments of the current disclosure include an electricmachine. As used herein, an electric machine (or electrical machine) maybe device that operates based on electromagnetic forces. In general, anytype of electromechanical energy converter that operates on, orgenerates, electricity may be an electric machine. Although notrequired, in some embodiments, the electric machine may be an electricmotor or an electric generator. During operation, an electric machinegenerates magnetic flux. In a radial flux electric machine, at leastsome portions of the generated magnetic flux may extend perpendicular tothe axis of rotation of the machine. Electric machines may include astator and a rotor separated by an air gap. In a radial flux electricmachine, the working (or main) magnetic flux may extend between therotor and the stator through the air gap in the radial plane.

FIGS. 53, 54, and 55 depict different views of an exemplary electricmachine 10. Exemplary electric machine 10 may include a stator 100, arotor 200, a base plate 56, a plurality of teeth 120, andelectromagnetic coils 300. Electric machine 10 may be an air-cooledsystem with a housing 50. External ribs 52 may be positioned on thesurface of the housing 50 between an end shield 54 and a stator baseplate 56. As illustrated in FIG. 53 , the stator base plate 56 mayinclude a plurality of pins 58 extending therefrom. The external ribs 52and the pins 58 may assist in transferring the heat generated by theelectric machine 10 during operation to the surrounding air. In thediscussion below, electric machine 10 in the form of an electric motorwill be described. However, the description is equally applicable toother types of electric machines, such as, for example, an electricgenerator. When electric machine 10 operates, its shaft 20 may rotate.The components of electric machine 10 will be described in greaterdetail below.

Electric machines of the current disclosure may include a rotorconfigured to rotate about an axis of rotation and a stator having aplurality of teeth annularly arranged on a stator core about the axis ofrotation. In general, a stator may be any stationary component (orassembly of components) of an electric machine and a rotor may be anyelectric machine component (or assembly of components) that isconfigured to move with respect to the stator. In some embodiments, thestator may be fixedly positioned with respect to the rotor. In someembodiments, the rotor may be configured to rotate about an axis ofrotation with respect to the stator. The rotor may be coupled to a shaft(rotor shaft) that rotates with the rotor. The axis about which therotor (and the shaft) rotates may be referred to as the “axis ofrotation.” As used herein, a plurality of teeth may refer to projectionsthat protrude from a body. The teeth may include a series ofsubstantially similar projections that protrude from the body. Forexample, in embodiments where the stator includes teeth, a series ofsubstantially similar projections that protrude from a body or core ofthe stator may include the teeth. Additionally, or alternatively, inembodiments where the rotor includes teeth, a series of substantiallysimilar projections that protrude from a body or core of the rotor mayinclude the teeth. In a radial flux electric machine, the teeth mayprotrude in the radial plane. In other words, the teeth in the radialplane may protrude (inward or outward) in the radial direction. Eachprojection may form a tooth. Typically, the projections (or teeth) maybe configured or shaped to direct a substantial portion of the magneticflux between the stator and the rotor.

A stator core may refer to a main body of the stator which may be madeof a single or multiple parts and may support and protect the rotatingmagnetic field. The stator core may be made of soft magnetic materialfor conducting the magnetic flux of an electric machine. A plurality ofteeth annularly arranged on the stator core about an axis of rotationmay refer to the teeth protruding from the core in a radial plane aboutthe axis of the rotor shaft of the rotating electric machine. In someembodiments, a stator core may include an annular stator ring thatextends around the axis of rotation and each tooth of the plurality ofteeth may include a core tooth-portion integral with the annular statorring. An annular stator ring may refer to a ring-shaped structure. Thering-shaped structure may be disposed around the axis of rotation of theelectric machine. A core tooth-portion may refer to the part protrudingfrom the annular stator ring of the stator ring in the radial plane. Theterm “integral” may be used herein to indicate that two parts areconnected to form a single part that practically cannot be dismantledwithout destroying the integrity of the part. In some cases, the twointegrally formed parts may be formed as a single part. Additionally, oralternatively, each tooth of the plurality of teeth may include one ormore additional tooth-portions non-integrally formed with the coretooth-portion. The one or more additional tooth-portions beingnon-integrally formed with the core tooth-portion may refer to the oneor more additional tooth-portions being attached together in a way thatthey may be easily separated from the annular stator ring. In someembodiments, the additional tooth-portions may be wedge-shaped. In someembodiments, a pair of additional tooth-portions may includetooth-portions arranged on opposite sides of the core tooth-portion. Asanother example, a pair of additional tooth-portions may also includetooth-portions arranged on the top and bottom surfaces of the coretooth-portion.

In certain embodiments, when all the tooth parts are assembled together,each tooth may define external surfaces having two sets of opposingfaces, the opposing faces of each set of the two sets being non-parallelto each other, and wherein each face of the two sets of opposing facesmay be inclined in a radial direction. That is, for example, for a toothhaving faces A-D, a pair of faces A and B may be non-parallel to eachother and another pair of faces C and D may be non-parallel to eachother. Additionally, or alternatively, the opposing faces of adjacentteeth may be substantially parallel to each other. That is, for example,face C of one tooth may be parallel to face D of an adjacent tooth. Theopposite side faces may be parallel to each other such that a slotformed between the adjacent teeth has a constant width in the radialdirection. In some embodiments, a cross-section of each tooth in a planeperpendicular to the radial direction may have a rectangular shape, anda perimeter of the cross-section may be substantially a constant in theradial direction and an area of the cross-section may vary in the radialdirection.

FIG. 53 illustrates a cross-sectional view of electric machine 10 alongan axial plane of the electric machine 10. In FIG. 53 , the axis ofrotation 1000 of electric machine 10 lies in the axial plane, and theaxial plane bisects the electric machine 10 into two symmetric halves.The radial plane extends perpendicular to the axis of rotation, and theaxis of rotation 1000 extends perpendicular (e.g., into and out of thepaper) to the radial plane. Electric machine 10 may include a stator 100and a rotor 200. The rotor 200 may be configured to rotate about theaxis of rotation 1000 with respect to the stator 100. The stator 100 mayinclude a stator core 110 including a plurality of teeth 120, and therotor 200 may include a rotor core 210 which is installed a plurality ofpermanent magnets 220. Electromagnetic coils 300 may be annularlymounted on the teeth 120 of the stator 100. The rotor 200 may beconnected to the shaft 20 that may be configured to rotate about theaxis of rotation 1000. When electric power is provided to theelectromagnetic coils 300, a magnetic field may be generated. Based onthe generated magnetic field, magnetic flux may flow between the rotor200 and the stator 100, thereby providing a rotary force to the rotor200. Electric machine 10 may be used as a power source in anyappropriate application. For example, in an automobile, the electricmachine 10 may drive the wheels of the automobile.

The stator 100 of electric machine 10 may include a plurality of teeth120 arranged annularly and symmetrically about the axis of rotation 1000on a stator core 110 of the stator 100. Each tooth 120 may includemultiple pieces or parts that may be arranged together to form acomposite or a multi-part tooth 120. Each tooth 120 may have arectangular or trapezoidal cross-sectional shape in both the axial planeand the radial plane. The width and length of each tooth 120 may vary inthe radial direction. That is, as illustrated in FIG. 53 , the length lof tooth 120 may vary from l₁ to l₂ in the radially outward direction oftooth 120 (along radial axis 2000) and the width of tooth 120 may varyin the radially outward direction of tooth 120 (not shown). In someembodiments, such as the electric machine 10 depicted in FIG. 54 , atooth may include a core tooth-portion 122 and a pair of additionaltooth-portions 124A and 124B positioned on opposite side surfaces of thecore tooth-portion 122.

The electric machines of the current disclosure may include a pluralityof electromagnetic coils. An electromagnetic coil (or an electric coil)may include one or more turns (or a winding) of an electrical conductorthat may generate a magnetic field when an electric current is passedthrough the conductor (e.g., in electric motors), or that may generate avoltage across the conductor when a magnetic field passes over the coil.In some embodiments, the turns of an electrical conductor may beconfigured or shaped like a coil. In some embodiments, anelectromagnetic coil may be an electrical conductor that contains aseries of conductive wires that may be configured to be wrapped around aferromagnetic core. In general, electromagnetic coils of the currentdisclosure may be associated with the stator or the rotor of theelectric machine. That is, in some embodiments, the plurality of coilsmay be coupled to (e.g., mounted, installed, wound on) the rotor and inother embodiments, the plurality of coils may be coupled to the stator.In some embodiments, each coil of the plurality of electromagnetic coilsmay be mounted on a separate tooth of the plurality of teeth. In theseembodiments, each tooth of the plurality of teeth protruding from thestator core may include an electromagnetic coil including one or moreturns of an electrical conductor.

FIG. 54 depicts a perspective view of the stator 100 of the exemplaryelectric machine 10 of FIG. 53 and FIG. 55 depict a cross-sectional viewof the stator 100 in the axial plane. Each electromagnetic coil 300 maybe mounted, or installed, on a tooth 120. In some embodiments, anelectromagnetic coil 300 may be installed on a tooth 120 such that theinner surface of the electromagnetic coil 300 fits snugly against anouter surface of the tooth 120. In some such embodiments, an externalshape (or profile) of the electromagnetic coil 300 may be substantiallythe same as the external shape of the tooth 120 that it is mounted on.Each tooth 120 of the stator 100 may be separated from an adjacent tooth120 by a slot 160 that may accommodate the electromagnetic coils 300mounted on the adjacent teeth 120. In embodiments where the toothincludes the core tooth-portion 122 and the additional tooth-portions124A and 124B, the core tooth-portion 122 of each multi-part tooth 120may be mounted on an electromagnetic coil 300 such that theelectromagnetic coil 300 extends around the core tooth-portion 122 withone or more gaps forming between the outer surfaces of the coretooth-portion 122 and the inner surface of the electromagnetic coil 300.In such embodiments, two gaps may be formed between the opposite sidesurfaces of the core tooth-portion 122 and the inner surface of theelectromagnetic coil 300, and one of the additional tooth-portions 124Aor 124B may be positioned in one gap and the other additionaltooth-portion 124B or 124A may be positioned in the other gap. It shouldalso be noted that, although the stator 100 is described as includingteeth 120, in some embodiments, the rotor 200 may alternatively oradditionally include teeth 120.

Electric machines of the current disclosure may include a base platelocated adjacent the plurality of electromagnetic coils and the statorcore. A base plate may refer to a piece or combination of parts attachedto the stator such that it may assemble the stator core andelectromagnetic coils on it. The base plate may be made ofheat-conducting materials to conduct and remove heat from its sources.For example, the base plate may be formed of aluminum. The base platemay be in thermal contact with the plurality of electromagnetic coilsand the stator core such that as the plurality of electromagnetic coilsand the stator core heat during operation, the base plate may beconfigured to serve as a common heat sink for the plurality ofelectromagnetic coils and the stator core. Thermal contact (or thermalconnection) refers to the proximity between the base plate and theplurality of electromagnetic coils such that good heat exchange occursbetween them. In some embodiments, when two bodies are in thermalcontact, or is thermally connected, heat exchange between the two bodiesoccur by conduction heat transfer mechanism. That is, the two bodies maybe in physical contact. Although the two bodies may be in directphysical contact when they are thermally connected (or are in thermalcontact), they do not have to be. For example, the two bodies in thermalcontact may be in physical contact with each other via a thermalinterfacial material (e.g., thermally conductive grease, etc.) disposedbetween the two bodies. If a thermal interface material is thusdisposed, conductive heat transfer occurs between the two bodies (inthermal contact) through the thermal interface material between them. Acommon heat sink may refer to a passive heat exchanger which maytransfer the heat generated by the plurality of electromagnetic coilsand the stator core to a fluid medium, for example, air or a liquidcoolant, where it may dissipate away from the electric machine, allowingregulation of the electric machine's temperature.

In some embodiments, each coil of the plurality of electromagnetic coilsand/or the stator core may be in contact with the base plate directly orthrough a thermally-conductive material disposed therebetween. Athermally-conductive material may refer to a material which improves theexchange and transfer of heat energy between systems. The abovedescribed thermal interface material may be a thermally-conductivematerial. The thickness of the thermally-conductive material and itsthermal conductivity may impact the exchange and transfer of heatenergy. As such, in some embodiments, the thermally-conductive materialdisposed between the plurality of electromagnetic coils and the statorcore and the base plate may be a thin layer of the thermally-conductivematerial to reduce its thermal resistance. The thickness of thethermally-conductive material depends on the application. Inapplications were the thermal conductivity of the thermally-conductivematerial is high, the thickness of the thermally-conductive material maybe higher.

In some embodiments, the electric machine may further include a motorhousing thermally connected to the base plate to enable heat generatedby the plurality of electromagnetic coils and stator core to bedissipated through the base plate and the motor housing. A motor housingmay refer to a casing which may be configured to accommodate the statorand rotor of the electric machine inside. A motor housing may be made ofheat-conducting material and contain ribs to increase the heat transfersurface. In some embodiments, the base plate may include a first sideand a second side opposite the first side, wherein the plurality ofelectromagnetic coils and the stator core may be in thermal contact withthe first side of the base plate and the motor housing may be in thermalcontact with the second side of the base plate. A side may refer to asurface of the base plate which may be upright, the top, the bottom, thefront, or the back of the base plate. In certain embodiments, the secondside of the base plate may include cooling fins that extend therefrom.Cooling fins may refer to surfaces extending from an object whichincrease the rate of heat transfer to or from the environment byincreasing convection. Cooling fins increase the surface area of anobject, which may result in an economical and satisfactory solution toheat transfer problems. Cooling fins may be made of a heat-conductingmaterial to increase the heat transfer surface. The cooling fins mayhave any shape and configuration. In some embodiments, the cooling finsmay include plate-like structures that protrude from the base plate. Insome embodiments, the cooling fins may include a plurality of pins. Pinsmay have any cross-sectional shape (e.g., circular, square, rectangular,etc.) and may enhance heat transfer from the surface by increasing thearea from which heat can be removed. In some embodiments, the pins mayrepresent an efficient cooling solution as they may have a large surfacearea in relation to other heat-sink methods. In addition, the spacingbetween the pins may allow air to flow through these spaces and createturbulence at the surface. The turbulence may assist in breaking up anyboundary layers that may exist at the surface of the fins (and increasethe convective heat transfer coefficient of the surface). Pin heat sinksmay consist of a base and an array of embedded pins, whose dimensions(e.g., length, thickness, density, material) may be customized to fitvarious applications depending on heat loads involved, available space,and airflow.

In some embodiments, the base plate may include a cylindrical hubportion extending around the axis of rotation. As used herein, acylindrical hub portion may refer to a portion of the base plate havinga cylindrical configuration which serves to fix the stator core. Thecylindrical hub portion may be made of heat-conducting material forconducting and removing heat from its sources. Additionally, the statorcore may include an annular stator ring that extends around thecylindrical hub portion of the base plate. As used herein, an annularstator ring may be a ring-shaped structure. The ring-shaped structuremay be disposed around the axis of rotation of the electric machine. Theannular stator ring extending around the cylindrical hub portion mayrefer to the annular stator ring completely or partially covering thecylindrical hub portion in such a way which surrounds the sides of thecylindrical hub portion. In some embodiments, an inner annular surfaceof the annular stator ring may be in contact with an outer annularsurface of the cylindrical hub portion of the base place directly orthrough a thermally-conductive material disposed therebetween. In someembodiments, the base plate may include air vents configured to directair to the plurality of electromagnetic coils when the rotor rotates.Air vents may refer to pathways, openings, cavities, or outlets thatallow entry of air therethrough. In some embodiments, the air vents maybe associated with vanes that operate similar to fan blades to blow airthrough the air vents. The air vents (and vanes if any) may be designedand configured to direct air flow to cool the electrical machine.

In FIGS. 54, 55, and 56 , electromagnetic coils 300 are shown to fittightly between the base plate 56 and teeth 120 of the stator 100. Theelectromagnetic coils 300 may be in direct contact with a first side 602of the base plate 56 and teeth 120 or may be in thermal contact with thefirst side 602 of the base plate 56 and teeth 120 via a thermallyconductive filler material. The stator core 110 may fit snugly against acylindrical hub portion 132 of the stator 100. The hub portion 132 maybe connected to the stator base plate 56. The base plate 56 and itscylindrical hub portion 132 may be made in the form of one single pieceor two separate parts and made of a heat-conducting material, forexample, aluminum. A second side 604 of the stator base plate 56 may beequipped with cooling fins made in the form of pins 58, which maysignificantly increase the cooling surface of the second side 604 of thestator base plate 56. The electromagnetic coils 300 may also fit tightlyor contact the teeth 120 of the stator core 110 on which they aremounted with the help of a thermally conductive filler. During operationof the electric machine, as schematically illustrated in FIG. 53 ,portion of the heat generated in the electromagnetic coils 300 (e.g.,due to electric current passing through the coils) may conduct throughthe teeth 120 and the cylindrical hub portion 132 to the base plate 56.

As also illustrated in FIG. 53 , a portion of the heat generated in thecoils 300 may conduct directly to the base plate 56 that is in thermalcontact therewith. In embodiments where the coils 300 are thermalcontact with the base plate 56 due to direct physical contact (betweenthe coils 300 and the base plate 56), heat from the coils 300 mayconduct directly into the base plate 56. In embodiments, where athermally-conductive material (or thermally conductive filler) isprovided between the coils 300 and the base plate 56, the heat from thecoils 300 may conduct into the base plate 56 through thethermally-conductive material. Thus, thermal contact between the coils300 and the base plate 56 provides an additional and shorter pathway forthe heat to conduct out of the coils 300. Since the coils 300 are inthermal contact with the base plate 56, heat may readily pass from thecoils 300 to the base plate 56 through this path. That is, as opposed tothe heat passing from the coils 300 into the base plate 56 via the tooth120 and the cylindrical hub portion 132, thermal contact between thecoils 300 and the base plate 56 provides a more direct heat conductionpathway to the base plate 56. Air flow across the pins 58 on the secondside 604 of the base plate 56 may then remove the heat from the baseplate 56.

Thus, it may be appreciated from the discussion above that the heatgenerated by the electromagnetic coils 300 and the stator core 110 withteeth 120 may be conducted through the stator base plate 56 and itscylindrical hub portion 132 and released into the environment. Inaddition, as illustrated in FIG. 53 , a portion of the heat from thestator base plate 56 may pass through the housing 50 connected to it andmay also be released into the environment through its outer ribbing 52.The housing 50 may be made of a thermally conductive material. Thestator base plate 56 may act as an air-cooled radiator for theelectrical machine 10. In addition, FIG. 53 depicts exemplary heatconduction paths 600 from the coil 300 to the base plate 56.

The inner surface of the housing 50 and/or the outer surface of therotor 200 may also have internal ribbing or fins (not shown). These finsfor an electric machine 10, much like ventilation holes, may be intendedto stir the air when the rotor 200 rotates. This may allow heat to beremoved from heating sources in the form of magnets and a rotor core andbe transferred to the housing 50 and further into the environment.

In the discussion above, electric machine 10 is described as being anair-cooled machine. However, this is only exemplary. In someembodiments, electric machine 10 may be liquid cooled. Electric machinesof the current disclosure may include a liquid-coolant channelconfigured to direct a cooling liquid therethrough. The cooling liquid(or coolant) may remove the heat generated by the coils 300 from theelectric machine. In some embodiments, the liquid-coolant channel may bedefined on the second side of the base plate such that as the coils andthe stator core heats during operation, the base plate is configured totransfer the heat to a liquid coolant in the liquid-coolant channel todissipate heat from the plurality of electromagnetic coils and thestator core. In some embodiments, the liquid-coolant channel may bedefined through the base plate. A liquid-coolant channel refers to acavity or a passageway that is configured to allow the flow of a liquidtherethrough. The liquid may be configured to remove the heat from thewalls of the channel. Any liquid that is configured to flow through theliquid-coolant channel may serve as the coolant. When the temperature ofthe liquid flowing through the channel is lower than the parts to becooled, the liquid removes the heat from the parts and thereby cools theparts. Any known liquid coolant (e.g., water, oil, glycol mixtures,dielectric fluid, etc.) may be directed through the liquid-coolantchannel.

In some embodiments, a wall of the liquid-coolant channel may be aportion of the second side of the base plate directly opposite a portionof the first side of the base plate that is in thermal contact with theplurality of electromagnetic coils. The liquid-coolant channel mayextend around the axis of rotation such that an annular region on thesecond side of the base plate may serve as a wall of the liquid-coolantchannel. Additionally, or alternatively, the annular region on thesecond side of the base plate may include a plurality of fins thatextend into the liquid-coolant channel. The plurality of fins may bearranged about the axis of rotation. The fins may increase the surfacearea from which heat can be removed by the liquid coolant flowing in theliquid-coolant channel. In some embodiments, the fins may be in the formof pins. As explained previously, the pins may be columnar projections(of any cross-sectional shape) that project into the liquid-coolantchannel from the second side of the base plate. In some embodiments, theliquid-coolant channel may have a coolant inlet and a coolant outlet.The coolant inlet may be configured to direct the coolant into theliquid-coolant channel and the coolant outlet may be configured todirect the coolant out of the liquid-coolant channel. Any aperture thatis configured to direct the coolant therethrough (e.g., into or out ofthe channel) may serve as the coolant inlet and the coolant outlet.

In some embodiments, the coolant intel and the coolant outlet may havefluid fittings (couplings, etc.) or may be otherwise configured todirect the coolant into and out of the channel in a hermetic manner. Insome embodiments, the coolant inlet and/or coolant outlet may be fluidlyconnected to a radiator or a heat exchanger. The heat exchanger may beconfigured to remove heat from the coolant. In some embodiments, thecoolant inlet, heat exchanger, and the coolant outlet may form a closedloop such that heated coolant from the coolant outlet is cooled in theheat exchanger and directed back into the electric machine through thecoolant inlet. Any type of heat exchanger may be used. In someembodiments, the coolant outlet may be fluidly connected to a commonheat exchanger (or radiator) of the system that the electric machine isa part of. For example, in embodiments where the electric machine ispart of an electric vehicle (e.g., used to power the wheels of theelectric vehicle), the coolant outlet may be connected to commonradiator of the electric vehicle. In some such embodiments, the liquidcoolant used to cool the electric machine may be a coolant that is usedto cool other components of the electric vehicle (or other system thatthe electric machine is a part of). It should be noted that although aliquid coolant is described above, in general, and fluid coolant (liquidor gas) may be used to cool the electric machine. In embodiments where agas coolant is used to cool the electric machine, the coolant gas may bedirected through the coolant channels in the base plate.

FIGS. 57-60 illustrate different views of exemplary liquid cooledelectric machines 700 of the current disclosure. FIG. 57 depicts anexemplary liquid-coolant channel 702 defined on the second side 604 ofthe stator base plate 56. Liquid-coolant channel 702 may be a cavitydefined between the second side 604 of the stator base plate 56 and acasing cover 712 of the housing 50. Channel 702 may extend around theaxis of rotation 1000 of the electric machine 700 to form an annularpassage that extends around the electric machine (see, e.g., FIG. 60 ).In some embodiments, as best seen in FIGS. 57 and 60 , the channel 702may be positioned directly below (or adjacent to) the coils 300 that aremounted on the multi-part teeth 120. The radial position (or the radialdistance from the axis of rotation 1000) of the channel 702 may besubstantially the same as that of the coils 300. As illustrated in FIG.57 , a radial dimension (e.g., radial width r₁) of the channel 702 mayalso be substantially the same as (or correspond to) the radialdimension (e.g., radial width r₂) of the coils 300. That is, the annularchannel 702 may trace a path that has substantially the same radial sizeas the coils 300 around the axis of rotation 1000 (see, e.g., FIG. 60 ).Although a single channel 702 is illustrated and described, this is onlyexemplary. In some embodiments, multiple coolant channels (e.g.,multiple radially spaced apart channels) may be provided. It should alsobe noted that although the channel 702 of FIG. 57 is defined between thesecond side 604 of the base plate 56 and the casing cover 712, this isonly exemplary. Many variations are possible. In some embodiments, thechannel 702 may extend through the base plate 56.

As shown in FIG. 57 , gaskets 706 may be provided between the base plate56 and the casing cover 712 to seal the channel 702 and prevent leaks.As shown in FIG. 57 , fins 716 may extend from second side 604 of thebase plate 56 into the channel 702 to increase the heat transfer surfaceof the base plate 56. The fins 716 may extend around the axis ofrotation 1000 to form radially spaced apart annular plates that projectinto the channel 702 from the base plate 56. As explained previously,the illustrated pattern of fins 716 is merely exemplary. Many otherpatterns are possible. In some embodiments, the fins 716 may beconfigured as pins. That is, multiple columnar projections may protrudeinto the channel 702 from the base plate 56. Although not visible inFIG. 57 , base plate 56 (and/or casing cover 712) may also include acoolant inlet that is configured to direct a coolant into the channel702 and a coolant outlet that is configured to direct the coolant out ofthe channel 702. In some embodiments, multiple coolant inlets and/oroutlets may be provided.

In some embodiments, liquid coolant channels may also extend throughother components of electric machine 700. FIGS. 58-60 illustrateexemplary liquid-coolant channels 704 through the cylindrical hubportion 132 of the stator 100. In some embodiments, channels for thepassage of liquid may also extend through stator core 110 and/or thehousing 50. The heat generated by the electromagnetic coils 300 and thestator core 110 (and/or other components) may pass (e.g., by conduction)through the stator base plate 56 and its cylindrical hub portion 132into liquid-coolant channels 702 and 704. The liquid flowing through thechannel 702, 704 may then transfer the heat to a radiator (not shown)for cooling. The cooled liquid from the radiator may be directed back tothe channels 702 and/or 704. In some embodiments, the liquid may flowthrough the channels 702 and/or 704 under pressure. In some embodimentsof an electric machine with an internal rotor 200, coolant channels forremoving heat may be located in the middle part of the housing 50 andits bearing parts.

Directly cooling the coils 300 of the electric machine by keeping thecoils 300 in thermal contact with the rotor base provide an additionaleasier path to cool the coils 300. That is, rather than relying on theheat form the coils 300 to be transferred to the external environmentvia the tooth 120, hub portion 132, and the base plate 56, keeping thecoils 300 in thermal contact with the base plate 56 enables easier andmore effective cooling of the coils 300. Improving the cooling ofelectric machines results in improvements in efficiency and power of theelectric machines.

The above-described embodiments of electric machine and related methodsare only exemplary. Many variations are possible. Some possiblevariations are described in U.S. Pat. Nos. 9,502,951 and 10,056,813,which are incorporated by reference in their entirety herein. Themethods described above need not be performed in the order discussed orindicated. Further, several steps may be omitted, combined, and/or somesteps added. Furthermore, although some aspects of the electric machineare described with reference to an electric machine of a particularconfiguration, the described aspects may be used in an electric machinehaving any configuration. Other embodiments of the electric machine andrelated methods will be apparent to those skilled in the art fromconsideration of the disclosure herein.

1-180. (canceled)
 181. A radial flux electric machine, comprising: arotor configured to rotate about an axis of rotation; a plurality ofelectromagnetic coils; a stator including an annular stator ringextending about the axis of rotation; and a plurality of multi-partteeth circumferentially arranged on the annular stator ring, eachmulti-part tooth of the plurality of multi-part teeth including a coretooth-portion integrally formed with and extending radially from theannular stator ring and at least one additional tooth-portion separatefrom the annular stator ring, wherein core tooth-portions of theplurality of multi-part teeth are circumferentially spaced apart fromeach other and the at least one additional tooth-portion of eachmulti-part tooth is disposed on an external surface of the coretooth-portion of that multi-part tooth, and wherein each coil of theplurality of electromagnetic coils is mounted on a different multi-parttooth of the plurality of multi-part teeth such that each coil surroundsa corresponding core tooth-portion of the multi-part tooth with a gapbetween the coil and the core tooth-portion, and the at least oneadditional tooth-portion is disposed in the gap.
 182. The electricmachine of claim 181, wherein the annular stator ring includes twomirror-symmetric halves coupled together along a plane of symmetryperpendicular to the axis of rotation.
 183. The electric machine ofclaim 182, wherein the two mirror-symmetric halves are attached togetheralong the plane of symmetry using an adhesive material.
 184. Theelectric machine of claim 182, wherein the annular stator ring includesa soft magnetic composite (SMC).
 185. The electric machine of claim 181,wherein the at least one additional tooth-portion includes a pair ofadditional tooth portions.
 186. The electric machine of claim 181,wherein the annular stator ring includes multiple axially stackedannular rings, and wherein at least two of the stacked annular rings aremade of a soft magnetic composite (SMC).
 187. The electric machine ofclaim 181, wherein the stator is positioned radially inwards of therotor and the core tooth-portion of each multi-part tooth extendsradially outward from the annular stator ring.
 188. The electric machineof claim 181, wherein the stator is positioned radially outwards of therotor and the core tooth-portion of each multi-part tooth extendsradially inward from the annular stator ring.
 189. The electric machineof claim 181, wherein a cross-sectional shape of the core tooth-portionand the at least one additional tooth-portion of each multi-part toothalong a plane perpendicular to a radial direction is substantiallyrectangular.
 190. The electric machine of claim 189, wherein across-sectional shape of the at least one additional tooth-portion alonga plane perpendicular to the axis of rotation is substantiallytriangular.
 191. The electric machine of claim 189, wherein across-sectional shape of each multi-part tooth of the plurality ofmulti-part teeth along a plane perpendicular to the axis of rotation issubstantially trapezoidal.
 192. The electric machine of claim 181,wherein the at least one additional tooth-portion includes a pair ofadditional tooth-portions arranged symmetrically on opposite sides ofthe core tooth-portion.
 193. The electric machine of claim 192, whereinthe pair of additional tooth-portions are arranged symmetrically about aplane perpendicular to the axis of rotation.
 194. The electric machineof claim 181, wherein the core tooth-portion and the at least oneadditional tooth-portion of each multi-part tooth of the plurality ofmulti-part teeth are coupled together using an adhesive material, and adifference between coefficients of thermal expansion of materials of thecore tooth-portion, the at least one additional tooth-portion, and theadhesive material is less than about 20%.
 195. The electric machine ofclaim 181, wherein the at least one additional tooth-portion of eachmulti-part tooth is wedged between an internal surface of a coil of theplurality of electromagnetic coils and an external surface of the coretooth-portion.
 196. The electric machine of claim 181, wherein a coil ofthe plurality of electromagnetic coils surrounds the core tooth-portionof each multi-part tooth such that at least two gaps are formed betweenan inner surface of the coil and opposite sides of the coretooth-portion, and wherein the at least one additional tooth-portionincludes at least two additional tooth-portions disposed in a differentgap of the at least two gaps.
 197. The electric machine of claim 181,wherein a cross-section of each multi-part tooth of the plurality ofmulti-part teeth in a plane perpendicular to a radial direction has arectangular shape.
 198. The electric machine of claim 181, wherein theelectric machine is an electric motor or an electric generator.
 199. Aradial flux electric machine, comprising: a rotor configured to rotateabout an axis of rotation; a plurality of electromagnetic coils; and astator having an annular stator ring and a plurality of coretooth-portions symmetrically arranged on the annular stator ring aboutthe axis of rotation to define a circumferential gap between adjacentcore tooth-portions and extending in a radial direction, wherein thestator includes a plurality of multi-part teeth with each tooth of theplurality of multi-part teeth including one core tooth-portion of theplurality of core tooth-portions and a pair of additional tooth-portionsnon-integrally formed with and attached to opposite external surfaces ofthe one core tooth-portion, and wherein a cross-sectional shape of eachtooth of the plurality of multi-part teeth in a plane perpendicular tothe axis of rotation is substantially trapezoidal.
 200. The electricmachine of claim 199, wherein the pair of additional tooth-portions aresymmetrically positioned about a plane perpendicular to the axis ofrotation.